diff --git a/04/main.go b/04/main.go
new file mode 100644
index 0000000..d90b179
--- /dev/null
+++ b/04/main.go
@@ -0,0 +1,135 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+func mustAtoi(line []rune) int {
+	i, _ := strconv.Atoi(string(line))
+	return i
+}
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+func makeScanner(test bool) *bufio.Scanner {
+	var f *os.File
+	if test {
+		f, _ = os.Open("inputs/testinput")
+	} else {
+		f, _ = os.Open("inputs/input")
+	}
+	reader := bufio.NewReader(f)
+	return bufio.NewScanner(reader)
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	sum := 0
+	for scanner.Scan() {
+		line := scanner.Text()
+		draws := map[int]struct{}{}
+		state := 0
+		acc := []rune{}
+		score := 0
+		for _, c := range line {
+			// slice off the 'game :' part
+			if state == 0 {
+				if c == ':' {
+					state = 1
+				}
+				continue
+			}
+			switch c {
+			case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+				acc = append(acc, c)
+			case '|':
+				state = 2
+				acc = []rune{}
+			case ' ':
+				if len(acc) != 0 && state == 1 {
+					draws[mustAtoi(acc)] = struct{}{}
+				} else if state == 2 {
+					if _, ok := draws[mustAtoi(acc)]; ok {
+						if score == 0 {
+							score = 1
+						} else {
+							score *= 2
+						}
+					}
+				}
+				acc = []rune{}
+			}
+		}
+		if _, ok := draws[mustAtoi(acc)]; ok {
+			if score == 0 {
+				score = 1
+			} else {
+				score *= 2
+			}
+		}
+		sum += score
+	}
+	fmt.Println(sum)
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+
+	card := 1
+	dupes := map[int]int{}
+	sum := 0
+	for scanner.Scan() {
+		line := scanner.Text()
+		draws := map[int]struct{}{}
+		state := 0
+		acc := []rune{}
+		score := 0
+		dupes[card]++
+		for _, c := range line {
+			// slice off the 'game :' part
+			if state == 0 {
+				if c == ':' {
+					state = 1
+				}
+				continue
+			}
+			switch c {
+			case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+				acc = append(acc, c)
+			case '|':
+				state = 2
+				acc = []rune{}
+			case ' ':
+				if len(acc) != 0 && state == 1 {
+					draws[mustAtoi(acc)] = struct{}{}
+				} else if state == 2 {
+					if _, ok := draws[mustAtoi(acc)]; ok {
+						score++
+					}
+				}
+				acc = []rune{}
+			}
+		}
+		if _, ok := draws[mustAtoi(acc)]; ok {
+			score++
+		}
+		for i := card + 1; i <= card+score; i++ {
+			dupes[i] += dupes[card]
+		}
+		sum += dupes[card]
+		card++
+	}
+	fmt.Println(sum)
+}