package main import ( "bufio" "bytes" "fmt" "io/ioutil" "strconv" "strings" ) func main() { nums := []int{} f, err := ioutil.ReadFile("input") if err != nil { panic(err) } reader := bufio.NewReader(bytes.NewReader(f)) for { line, err := reader.ReadString('\n') if err != nil { break } i, err := strconv.Atoi(strings.TrimSpace(line)) if err != nil { panic(err) } for _, num := range nums { if i+num == 2020 { fmt.Printf("%d", i*num) return } } nums = append(nums, i) } }