#include <iostream>
#include <cmath>

using namespace std;

const double N{15};

int main() {

    double stirlings{0};
    double actual{0};

    stirlings = exp( -N) * pow(N,N) * sqrt(2*M_PI*N);
    actual = 15.0*14.0*13.0*12.0*11.0*10.0*9.0*8.0*7.0*6.0*5.0*4.0*3.0*2.0;

    cout << N << "! by stirlings is " << stirlings << endl;
    cout << N << "! by calculation is " << actual << endl;

    return 0;
}