#include <iostream.h>

int factorial(int n);
//Returns factorial of n.
//The argument n should be nonnegative.

int main( )
{
    cout << "0! = " << factorial(0) << endl;
    cout << "1! = " << factorial(1) << endl;
    cout << "2! = " << factorial(2) << endl;
    cout << "3! = " << factorial(3) << endl;

    return 0;
}

int factorial(int n)
{
    int product = 1;
    while (n > 0)
    {
        product = n * product;
        n--;
    }

    return product;
}