Why does it keep saying wrong answer?

#include<stdio.h>
#include<math.h>

int main()

{
    int num,element_no;

    double sum;

    scanf("%d",&num);

    if(num<0)

    {
         element_no  = fabs(num) + 2;


    }

    else

    {
        element_no = num;
    }

    sum = (element_no/2.0) * (num + 1) ;


    int ans = sum;
    printf("%d\n",ans);

    return 0;
}