[백준] 5341번

import java.util.*;
import java.io.*;
import java.math.*;

public class Main {
   public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);

      while (true) {
         int N = sc.nextInt();

         if (N == 0) break;
         else {
            System.out.println((N * (N + 1)) / 2);
         }
      }
   }
}