class Answer {
	constructor(input) {
		this.data = Number(input);
		this.count = 0;
	}

	main() {
		for(let i=0;this.data>i;i++) {
			this.count += i + 1;
		}
		this.dest(this.count);
	}

	dest(ans) {
		console.log(ans);
	}
}
new Answer(require("fs").readFileSync("/dev/stdin", "utf8")).main();