#include <stdio.h>

int main(void){

  int n, sum = 0;

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

  if (n < 0){
    int i = 2 * n;
    while (i <= n) sum += i++;
  }
  else {
    int i = n; 
    while (i <= 2 * n) sum += i++;
  }

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

  return 0;
}