/**
 * Yukicoder1
 */
import java.util.*;
public class Yukicoder1 {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int sum = 0;
    int n = sc.nextInt();
    for (int i = 1; i <= n; i++) {
      sum += i;
    }
    System.out.println(sum);
  }
}