package main

import (
    "fmt"
    "os"
    "regexp"
    "strconv"
)

func check(e error) {
    if e != nil { panic(e) }
}

func main() {

    dat, err := os.ReadFile("data.txt")
    check(err)
    dat_str := string(dat)
    
    // get all numbers within mul(*,*) using capture groups
    r := regexp.MustCompile("mul\\(([0-9]{1,3}),([0-9]{1,3})\\)")
    matches := r.FindAllStringSubmatch(dat_str, -1)
    
    acc := 0
    for _, elem := range matches {
        // convert to numbers
        num1, err := strconv.Atoi(elem[1])
        check(err)
        num2, err := strconv.Atoi(elem[2])
        check(err)

        acc += num1 * num2
    }

    fmt.Println(acc)
}