#include <iostream>

using namespace std;

int n;

int cmmdc(int a, int b)
{
    int r;
    while(b != 0)
    {
        r = a % b;
        a = b;
        b = r;
    }
    return a;
}

int main()
{
    cout << cmmdc(12, 20);
    return 0;
}