const fs = require('fs')
const readline = require('readline');

const readInterface = readline.createInterface({
    input: fs.createReadStream('input'),
    console: false
});

let numbers = [];

readInterface.on('line', function(line) {
  numbers.push(Number(line));
});

readInterface.on('close', function(line) {
  numbers.forEach(function(a) {
    numbers.forEach(function(b) {
      if (a + b == 2020) {
        console.log(a*b);
        process.exit();
      }
    });
  });
});