sum of product mod plus function

#include <stdio.h>

long long SumOfProduct(long long n)
{
    long long r, q = n, s = 0;
    while(q > 0) {
        r = q % 10;
        s += r;
        q /= 10;
    }
    return s;
}

int main()
{
    long long x; // as x <= 10^19
    scanf("%lld", &x);

    long long sum;

    sum = SumOfProduct(x);

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


    return 0;
}