#include <iostream>

using namespace std;

int nwd( int a, int b){
int r=a % b;
while (r!=0)
{
    a=b;
    b=r;
    r=a % b;
}
return b;
}
int main()
{
    cout << "Hello world!" << endl;

    int r=nwd ( 5, 10);
    cout << r << endl;
    return 0;
}