10分钟一次性AC。

#include<iostream>
using namespace std;
int gcd(int a, int b)
{
    int c=-1;
    while(c!=0)
    {
        c=a%b;
        if(c!=0)
        {
            a=b;
            b=c;
        }
    }
    return b;
}
int main()
{
    //freopen("xxx.in","r",stdin);
    //freopen("yyy.out","w",stdout);
    int n,m;
    cin >> n >> m;
    cout << gcd(n,m);
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}