https://www.acmicpc.net/problem/8393
const fs = require("fs");
let input = (process.platform === "linux"
? fs.readFileSync("/dev/stdin").toString()
: `3`
).trim();
const number = parseInt(input);
let answer = 0;
for (let i = 1; i <= number; i++) {
answer = answer + i;
}
console.log(answer);