#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  int i = 0;
  int n = 0;
  int r = 0;

  scanf("%d", &n);

  for (i = 0; i <= n; i++) {
    r = r + i;
  }

  printf("%d", r);

  return 0;
}