'use strict'

function main(s) {  
  
  // 入力処理
  const input = Number(s.replace(/\n/g, ''));
  const result = new Array(input).fill(0).map((x, i) => i + 1).reduce((a, b) => a + b);
  console.log(result);
}

main(require("fs").readFileSync("/dev/stdin", "utf8"));
