#include<stdio.h>
#include<math.h>
int main()
{
    int N,i,sum;
    scanf("%d",&N);
    if(abs(N)<= 10000){
    if(N > 0){
      sum = (N * (N + 1))/2;
    }
     else if(N < 0)
    {
      sum = ((abs(N)+2) * (N + 1))/2;
    }
    printf("%d",sum);
    }
    return 0;
}

Edited by author 19.06.2018 15:45

Edited by author 19.06.2018 15:45