package main

import (
	"fmt"
	"io/ioutil"
	"strconv"
	"strings"
)

func main() {
	data, _ := ioutil.ReadFile("in1.txt")
	s := strings.Split(string(data), "\n")
	var nums []int
	for _, st := range s {
		n, _ := strconv.Atoi(st)
		nums = append(nums, n)
	}
	for _, n := range nums {
		for _, n2 := range nums {
			if n2 != n {
				if n2+n == 2020 {
					fmt.Println(n * n2)
					return
				}
			}
		}
	}
}