fact sda

#include <stdio.h>
#include <stdlib.h>
typedef unsigned long long ull;

ull fact(ull x) {
    if (x == 0) {
        return 1;
    }
    ull ans = 1;
    for (ull i = 2; i <= x; i++) {
        ans *= i;
    }
    return ans;
}

int main(void) {
    ull x;
    scanf_s("%llu", &x);
    printf("%llu", fact(x));
    return 0;
}