#include <iostream>
#include <conio.h>

using namespace std;

double multiply (int a){
    double multiply = 1;
    for (int c = 2; c <= a; c += 2){
        double z = c  / (c - 1.) * c / (c + 1);
        multiply = multiply * z;
    }
    return multiply;
}

double multiply_r (int a){
    if (a == 0)
        return 1;
    return a  / (a - 1.) * a / (a + 1) * multiply_r(a - 2);
}

int main(){
    int a,b;
    do{
        cout << "Enter a multiple of 2 and >= 2, please." << endl;
        cin >> a;
    }
    while (a&1 || a < 2);
    cout << "Enter 0 to count recursively, otherwise it will be counted normally." << endl;
    cin >> b;
    (b == 0) ? (cout << "Answer is '"<< multiply_r(a) << "'"<< endl) : (cout << "Answer is '" << multiply(a) << "'"<< endl);
    cout << "Press any key for end program.";
    getch();
}