#include <iostream>
#define ll long long
using namespace std;

ll zhanzhuan(ll,ll);

int main(){
	std::ios::sync_with_stdio(false);cin.tie(0),cout.tie(0);
	ll a,b;
	cin >> a >> b;
	if(a>b){
		ll t;
		t=a;
		a=b;
		b=t;
	}
	cout << zhanzhuan(a,b);
	return 0;
}
ll zhanzhuan(ll a,ll b){
	if(b==0){
		return a;
	}
	else{
		return zhanzhuan(b,a%b);
	}
}

b站翁恺老师讲的辗转相除法

#include <stdio.h>

int main()

{

int n,m;

scanf("%d%d",&n,&m);

int a;

while(m!=0){

a=n%m;

n=m;

m=a;

}

printf("%d",n);

return 0;

}

#include <stdio.h> int main() { int a,b,t; scanf("%d %d",&a,&b); while (b!=0){ t=a%b; a=b; b=t;

}
printf("%d",a);
return 0;

}