package yukicoder;

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

public class YukiCoder480 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		// Read INPUT
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		try {
			// translate Integer
			int N = Integer.parseInt(br.readLine());
			
			int ans=0;
			// Calculate
			for(int i=1; i<=N; i++) {
				ans+=i;
			}
			
			// output ANSWER
			System.out.println(ans);
			
		} catch(Exception e) {
			System.out.println("error");
		}
		
		return;

	}

}