/*
使用递归计算1到n的和
*/
public class Test3
{
  public static void main(String[] args){
  java.util.Scanner s = new java.util.Scanner(System.in);
  int n = s.nextInt();
  int s = sum(n);
  }

  public static int sum(int n){
    if(n == 1)
    return 1;
  return n = n + sum(n - 1);
  }
}