diff --git a/days/src/main/kotlin/Day18.kt b/days/src/main/kotlin/Day18.kt
new file mode 100644
index 0000000..e442793
--- /dev/null
+++ b/days/src/main/kotlin/Day18.kt
@@ -0,0 +1,165 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import be.vandewalleh.aoc.utils.input.createDay
+import java.util.*
+
+enum class Operator { Add, Multiply }
+
+operator fun Operator.invoke(a: Long, b: Long) = when (this) {
+    Operator.Add -> a + b
+    Operator.Multiply -> a * b
+}
+
+@Day(18)
+class Day18(@Lines val input: Input<List<String>>) {
+
+    val lines = input.value.map { it.replace(" ", "") }
+
+    private fun parseGroups(line: String): Map<Int, List<IntRange>> {
+        var depth = 0
+        val groups = mutableMapOf<Int, MutableList<IntRange>>()
+        val openingPars = Stack<Int>()
+
+        for ((index, char) in line.withIndex()) {
+            when (char) {
+                '(' -> {
+                    openingPars.push(index)
+                    depth++
+                }
+                ')' -> {
+                    depth--
+                    val group = groups.getOrPut(depth) { mutableListOf() }
+                    group.add(openingPars.pop()..index)
+                }
+            }
+        }
+
+        check(openingPars.isEmpty())
+        return groups.also { println(it) }
+    }
+
+    private fun solveGroup(group: String, precedence: Boolean) = solveGroup(parseGroup(group), precedence)
+
+    private tailrec fun solveGroup(group: Pair<LinkedList<Long>, LinkedList<Operator>>, precedence: Boolean): Long {
+        val (operands, operators) = group
+        println(operands)
+        println(operators)
+
+        if (!precedence) {
+            for (i in operators.indices) {
+                val a = operands[i]
+                val b = operands[i + 1]
+
+                val result = operators[i](a, b)
+
+                operands[i + 1] = result
+            }
+
+            return operands.last()
+        } else {
+
+            var i = 0
+            while (operators.any { it == Operator.Add }) {
+
+                val a = operands[i]
+                val b = operands[i + 1]
+                val operator = operators[i]
+
+                if (operator == Operator.Add) {
+                    val res = operator(a, b)
+                    operands.removeAt(i)
+                    operands[i] = res
+                    operators.removeAt(i)
+                    i--
+                }
+
+                i++
+            }
+
+            return solveGroup(operands to operators, precedence = false)
+        }
+    }
+
+    private fun parseGroup(group: String): Pair<LinkedList<Long>, LinkedList<Operator>> {
+        val operands = LinkedList<Long>()
+        val operators = LinkedList<Operator>()
+        val operand = StringBuilder()
+
+        for (char in group) {
+            if (char.isDigit()) {
+                operand.append(char)
+            } else {
+                val operator = when (char) {
+                    '+' -> Operator.Add
+                    '*' -> Operator.Multiply
+                    else -> error("Unknown operator $char")
+                }
+                operators.add(operator)
+                operands.add(operand.toString().toLong())
+                operand.clear()
+            }
+        }
+
+        operands.add(operand.toString().toLong())
+
+        check(operands.size == operators.size + 1)
+        check(operators.isNotEmpty())
+        return Pair(operands, operators)
+    }
+
+    private fun solveLine(line: String, precedence: Boolean = false): Long {
+        var l = line
+
+        while (true) {
+            val groups = parseGroups(l)
+            if (groups.isEmpty()) break
+
+            val highestDepth = groups.keys.sorted().maxOrNull()!!
+            val solvableRanges = groups[highestDepth]!!
+
+            val solved = ArrayDeque<Pair<IntRange, Long>>()
+
+            for (range in solvableRanges) {
+                val rangeWithoutPars = range.first + 1 until range.last
+                val answer = solveGroup(l.substring(rangeWithoutPars), precedence)
+                solved.addLast(range to answer)
+            }
+
+            var solution = solved.removeFirst()
+            var inside = false
+
+            val builder = StringBuilder()
+
+            for (i in l.indices) {
+                if (!inside && i in solution.first) {
+                    inside = true
+                    builder.append(solution.second)
+                } else if (inside && i !in solution.first) {
+                    inside = false
+
+                    solution = if (solved.isEmpty()) -1..-1 to -1  // avoid null checks..
+                    else solved.removeFirst()
+
+                    builder.append(l[i])
+                } else if (i !in solution.first) {
+                    builder.append(l[i])
+                }
+            }
+
+            l = builder.toString()
+        }
+
+        return solveGroup(l, precedence)
+    }
+
+    fun part1() = lines.sumOf { solveLine(it) }
+    fun part2() = lines.sumOf { solveLine(it, precedence = true) }
+}
+
+fun main() = with(createDay<Day18>()) {
+    println(part1())
+    println(part2())
+}
diff --git a/days/src/main/resources/day18.txt b/days/src/main/resources/day18.txt
new file mode 100644
index 0000000..4260b88
--- /dev/null
+++ b/days/src/main/resources/day18.txt
@@ -0,0 +1,372 @@
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diff --git a/days/src/test/kotlin/Day18Test.kt b/days/src/test/kotlin/Day18Test.kt
new file mode 100644
index 0000000..e98dc05
--- /dev/null
+++ b/days/src/test/kotlin/Day18Test.kt
@@ -0,0 +1,23 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Input
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.CsvSource
+
+class Day18Test {
+
+    @CsvSource(value = [
+        "1 + 2 * 3 + 4 * 5 + 6 , 231",
+        "1 + (2 * 3) + (4 * (5 + 6)) , 51",
+        "2 * 3 + (4 * 5) , 46",
+        "5 + (8 * 3 + 9 + 3 * 4 * 3) , 1445", // !!!
+        "5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4)) , 669060",
+        "((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2 , 23340"
+    ])
+    @ParameterizedTest
+    fun examplesPart2(input: String, output: Long) {
+        val day18 = Day18(Input(listOf(input)))
+        assertThat(day18.part2()).isEqualTo(output)
+    }
+}