function Main(input) {
	//input = input.split("\n");
	//tmp1 = parseInt(input[0]);
	//tmp2 = input[1].split(" ");

	var input = parseInt(input);
	var ans = 0;

	for (i = 0; i <= input; i++) {
		ans += i;
	}

	console.log('%d', ans);

}

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