sum of even minus odds

#include<stdio.h>

int main()
{



    int i, n, sum = 0, substract = 0;
    scanf("%d", &n);

    for(i = 1; i <= n; i++)
    {
        if(i % 2 == 0)
        {
            sum = sum + i;
        }
        else
        {
           substract = sum - i;
        }
    }
    printf("Sum = %d\n", sum);
    printf("Substract = %d\n", substract);



    return 0;
}