const lineIter = (function* () {
  const stdin = require('fs').readFileSync(process.stdin.fd, 'utf8');
  const lines = stdin.trim().split('\n');
  for (const line of lines) {
    yield line.trim();
  }
})();
const wordIter = (function* () {
  while (true) {
    const { done, value: line } = lineIter.next();
    if (done) {
      break;
    }
    const words = line.split(' ');
    for (const word of words) {
      yield word;
    }
  }
})();
const read = () => wordIter.next().value;

const main = async () => {
  const n = parseInt(read());

  const sum = Array(n)
    .fill()
    .map((_, i) => i + 1)
    .reduce((acc, num) => acc + num, 0);

  console.log(`${sum}`);
};

(async () => {
  try {
    await main();
  } catch (e) {
    console.error(e);
  }
})();