//No.480 合計
//https://yukicoder.me/problems/no/480
//20170417 1519

package no480;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class No480 {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String inLine;
		int n;
		int sum = 0;

		inLine = br.readLine();
		
		n = Integer.parseInt(inLine);
		
		for(int i = 1; i <= n; i++){
			sum += i;
		}
		System.out.print(sum);
	}
}