function Main(input) {
  // parse input
  const n = parseInt(input);

  // solve
  const c = solve(n);

  // output
  console.log(c);
}

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

function solve(n) {
  let result = 0;
  for (let i = 1; i <= n; i++) {
    result += i;
  }
  return result;
}