//==============================================================================
///
/// File:           fac2.cpp
/// Author:         Gerald Broughton
/// Date Created:   10/25/2011
/// Changes:        -none-
///
//==============================================================================

#include <iostream>

using namespace std;

double factorial(double n){
    double ans = 1;
    for(double i = 2; i <= n; ++i){
        ans *= i;
        if(ans < 0 || ans > 7.25742e+306)
            return -1;
    }
    return ans;
}

int main(){
    cout << "Factorial of: " << flush;
    double n;
    if(cin >> n){
        if(n >= 0 && n != 9999){
            double fact = factorial(n);
            if(fact < 0){
                cerr << "overflow error: " << n << " is too big." << endl;
            }else{
                cout << n << "! is " << fact << endl;
            }
        }else{
            cerr << "\aUndefined: factorial of a negative number " << n << endl;
        }
    }
}