#include <stdio.h>

int main(void){

  int n, sum = 0, i;

  printf("Enter a positive or negative integer:\n");
  scanf("%d", &n);

  if (n < 0)
    for(i = 2 * n; i <= n; i++) sum += i;
  else 
    for(i = n; i <= 2 * n; i++) sum += i; 

  printf("%d \n", sum);

  return 0;
}