#include <stddef.h>
#include <stdio.h>

#define N 6

size_t factorial(size_t n)
{
    size_t res = 1;

    for (size_t i=2; i<=n; ++i) {
        res *= i;
    }
    return res;
}

int main()
{
    printf("result = %zu\n", factorial(N));

    return 0;
}