diff --git a/05/main.go b/05/main.go
new file mode 100644
index 0000000..7453627
--- /dev/null
+++ b/05/main.go
@@ -0,0 +1,145 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func must[T, Q any](f func(T) (Q, error), t T) Q {
+	q, err := f(t)
+	if err != nil {
+		panic(err)
+	}
+	return q
+}
+
+func iter[T, Q any](f func(T) Q, t []T) []Q {
+	r := make([]Q, len(t))
+	for i := 0; i < len(t); i++ {
+		r[i] = f(t[i])
+	}
+	return r
+}
+
+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)
+
+	seeds := [][]int{}
+	scanner.Scan()
+	line := scanner.Text()
+	_, seedList, _ := strings.Cut(line, ": ")
+	for _, s := range strings.Split(seedList, " ") {
+		seeds = append(seeds, []int{must(strconv.Atoi, s)})
+	}
+	scanner.Scan() // discard empty line
+
+	state := 1
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			for i, s := range seeds {
+				if len(s) == state {
+					seeds[i] = append(seeds[i], s[state-1])
+				}
+			}
+			state++
+			continue
+		}
+		if line[len(line)-1] == ':' {
+			continue
+		}
+		// destination, source, length
+		m := iter(
+			func(s string) int { return must(strconv.Atoi, s) },
+			strings.Split(line, " "),
+		)
+		for i, s := range seeds {
+			if len(s) == state && m[1] <= s[state-1] && m[1]+m[2] > s[state-1] {
+				seeds[i] = append(seeds[i], s[state-1]-m[1]+m[0])
+			}
+		}
+	}
+	lowest := seeds[0][len(seeds[0])-1]
+	for _, s := range seeds {
+		if s[len(s)-1] < lowest {
+			lowest = s[len(s)-1]
+		}
+	}
+	fmt.Println(lowest)
+}
+
+func partTwo() {
+	scanner := makeScanner(true)
+
+	seeds := [][]int{}
+	scanner.Scan()
+	line := scanner.Text()
+	_, seedRanges, _ := strings.Cut(line, ": ")
+	r := strings.Split(seedRanges, " ")
+	for i := 0; i <= len(r); i += i + 2 {
+		rng := must(strconv.Atoi, r[i+1])
+		for j := 0; j < rng; j++ {
+			// this is too slow!
+			seeds = append(seeds, []int{must(strconv.Atoi, r[i]) + j})
+		}
+	}
+	scanner.Scan() // discard empty line
+
+	state := 1
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			for i, s := range seeds {
+				if len(s) == state {
+					seeds[i] = append(seeds[i], s[state-1])
+				}
+			}
+			state++
+			continue
+		}
+		if line[len(line)-1] == ':' {
+			continue
+		}
+		// destination, source, length
+		m := iter(
+			func(s string) int { return must(strconv.Atoi, s) },
+			strings.Split(line, " "),
+		)
+		for i, s := range seeds {
+			if len(s) == state && m[1] <= s[state-1] && m[1]+m[2] > s[state-1] {
+				seeds[i] = append(seeds[i], s[state-1]-m[1]+m[0])
+			}
+		}
+	}
+	lowest := seeds[0][len(seeds[0])-1]
+	for _, s := range seeds {
+		if s[len(s)-1] < lowest {
+			lowest = s[len(s)-1]
+		}
+	}
+	fmt.Println(lowest)
+}
diff --git a/go.mod b/go.mod
index a3f7ee9..be9315c 100644
--- a/go.mod
+++ b/go.mod
@@ -1 +1,3 @@
 module git.yetaga.in/alazyreader/AdventOfCode2023
+
+go 1.21.4