#include <iostream>

using namespace std;

int gcd(int m, int n);

int gcd(int m, int n)
{
    if (m <= 0 || n <= 0)
        return 0;

    if (m % n == 0)
        return n;
    else
        return gcd(n, m%n);
}

int main(int argc, const char *argv[])
{
    int m, n;
    int result;
    cout << "Enter 2 numbers to calculate the greatest common divisor (0 to quit)" << endl;
    do {
        cout << ">> ";
        cin >> m >> n;
        if (m <= 0 || n <= 0) {
            cout << "Please input positive numbers (0 to quit)" << endl;
        } else {
            result = gcd(m, n);
            cout << "gcd(" << m << ", " << n << ") = " << result << endl;
        }
    } while (m != 0 || n != 0);

    return 0;
}