#define int long long
using namespace std;


int gcd(int a,int b){
	if(b==0){
		return a;
	}else{
		return gcd(b,a%b);
	}
}

signed main()
{
	
	int a,b;
	cin>>a>>b;
	cout<<gcd(a,b); 
	return 0;
}

#include <bits/stdc++.h>

using namespace std;

using ll =long long; ll gcd (ll a,ll b){

if(b==0){
	return a;
}
return gcd (b,a%b);

}

int main(){ ll a,b; //主函数力还得定义 cin>>a>>b; cout<< gcd(a,b) <<endl;

return 0; 

}

oi-wiki

#include <iostream>
#include <cmath>

using namespace std;

using ll = long long;

ll fxxk(ll a, ll b) {
	return b == 0 ? a : fxxk(b, a % b);
}

int main() {
	ll a, b;
	cin >> a >> b;
	cout << fxxk(a, b) << '\n';
	return 0;
}