function main(input = "") {
  if (!input) throw Error;

  let sum = 0;

  for (let i = 1; i <= parseInt(input); i++) {
    sum += i;
  }

  return sum;
}

const { readFileSync, existsSync } = require("fs");
const stdin = "/dev/stdin";

if (existsSync(stdin)) {
  const input = readFileSync(stdin, "utf8");
  console.log(main(input));
}

module.exports = main;