diff --git a/Sources/aoc2021/03.swift b/Sources/aoc2021/03.swift
index f088608..98d5d00 100644
--- a/Sources/aoc2021/03.swift
+++ b/Sources/aoc2021/03.swift
@@ -6,7 +6,6 @@
 //
 
 import Foundation
-import AppKit
 
 struct Day03 {
     let inputPath: String
diff --git a/Sources/aoc2021/04.swift b/Sources/aoc2021/04.swift
new file mode 100644
index 0000000..f38d17a
--- /dev/null
+++ b/Sources/aoc2021/04.swift
@@ -0,0 +1,87 @@
+//
+//  File.swift
+//  
+//
+//  Created by Max Nuding on 04.12.21.
+//
+
+import Foundation
+
+struct Board {
+    var numbers: [[Int?]]
+    var hasWon = false
+    
+    mutating func crossOf(num: Int) -> Bool {
+        for (rowNumber, row) in numbers.enumerated() {
+            if let colNumber = row.firstIndex(of: num) {
+                numbers[rowNumber][colNumber] = nil
+                //print("Found at: \(rowNumber),\(colNumber)")
+                return true
+            }
+        }
+        return false
+    }
+    
+    mutating func checkHasWon() -> Bool {
+        //print("HasWon?: \(numbers)")
+        let foundInRows = numbers.contains { row in
+            row.allSatisfy { $0 == nil }
+        }
+        if foundInRows {
+            return true
+        }
+        let foundInColumns = numbers.indices.contains { columnIndex in
+            return numbers.allSatisfy { $0[columnIndex] == nil }
+        }
+        hasWon = foundInColumns
+        return hasWon
+    }
+    
+    func calculateScore() -> Int {
+        numbers
+            .reduce([], +)
+            .compactMap { $0 }
+            .reduce(0, +)
+    }
+}
+
+struct Day04 {
+    let inputPath: String
+    
+    func run() {
+        let input = try! String(contentsOfFile: inputPath)
+        var lines = input
+            .components(separatedBy: .newlines)
+        let inputNumbers = lines
+            .removeFirst()
+            .split(separator: ",")
+            .map { Int($0)! }
+        _ = lines.removeFirst() //empty seperator line
+        
+        let boards = lines
+            .split(separator: "")
+            .map { boardLines in
+                Board(numbers: boardLines.map { $0.split(separator: " ").map { num in Int(num)! } })
+            }
+        var boardsA = boards
+        runA(boards: &boardsA, inputNumbers: inputNumbers)
+    }
+    
+    func runA(boards: inout [Board], inputNumbers: [Int]) {
+        for inputNumber in inputNumbers {
+            //print("\nInput: \(inputNumber)")
+            for (idx, var board) in boards.enumerated() {
+                //print("Checking board: \(idx)")
+                if board.crossOf(num: inputNumber) && board.checkHasWon() {
+                    print(board.calculateScore() * inputNumber)
+                    return
+                }
+                boards[idx] = board
+            }
+        }
+    }
+    
+    func runB(_ commands: [String]) {
+        
+    }
+}
diff --git a/Sources/aoc2021/Resources/input/04.txt b/Sources/aoc2021/Resources/input/04.txt
new file mode 100644
index 0000000..669a51d
--- /dev/null
+++ b/Sources/aoc2021/Resources/input/04.txt
@@ -0,0 +1,19 @@
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7
diff --git a/Sources/aoc2021/main.swift b/Sources/aoc2021/main.swift
index fec7edd..fb2acec 100644
--- a/Sources/aoc2021/main.swift
+++ b/Sources/aoc2021/main.swift
@@ -20,6 +20,7 @@ let execTimeMs = round((end - start) * 1000.0 * 100.0) / 100.0
 print("Finished in \(execTimeMs)ms")
 */
 
+/*
 print("Starting day 03")
 let input03 = Bundle.module.path(forResource: "03", ofType: ".txt")!
 let start = CFAbsoluteTimeGetCurrent()
@@ -27,3 +28,12 @@ Day03(inputPath: input03).run()
 let end = CFAbsoluteTimeGetCurrent()
 let execTimeMs = round((end - start) * 1000.0 * 100.0) / 100.0
 print("Finished in \(execTimeMs)ms")
+*/
+
+print("Starting day 04")
+let input03 = Bundle.module.path(forResource: "04", ofType: ".txt")!
+let start = CFAbsoluteTimeGetCurrent()
+Day04(inputPath: input03).run()
+let end = CFAbsoluteTimeGetCurrent()
+let execTimeMs = round((end - start) * 1000.0 * 100.0) / 100.0
+print("Finished in \(execTimeMs)ms")