参考答案：

#include<iostream>
using namespace std;
typedef long long LL;
LL gcd(LL a, LL b)
{
    return b ? gcd(b, a % b) : a;
}
int main()
{
    LL a, b;
    cin >> a >> b;
    cout << gcd(a, b) << endl;

    return 0;
}