序列求和

/**

 * 求1+2+3+...+n的值

 */

import java.io.*;

public class 序列求和 {

public static void main(String args[]) throws  IOException{
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
long i = Integer.parseInt(in.readLine());
long sum = (1+i)*i/2;
System.out.println(sum);
}

}