>>883
手抜きver
#include<stdio.h>
int gcd(int a,int b){
    if(a <= 0 || b <= 0)return -1;
    while(a%=b)if((b%=a)==0)return a;
    return b;
}
int main(){
    int m, n;
    scanf("%d %d", &m, &n);
    printf("%d\n", gcd(m,n));
    return 0;
}