C :

#include<stdio.h> 
int Gcd(int a,int b); 
int main() 
{ 
    int m,n; 
    scanf("%d,%d",&m,&n); 
    printf("%d\n",Gcd(m,n)); 
    return 0; 
} 
int Gcd(int a,int b) 
{ 
    int r,temp; 
    r=a%b; 
    if(r==0) 
        return b; 
    else 
	do{
        temp=b; 
        b=r; 
        a=temp; 
        r=a%b; 
    }while(r!=0); 
    return b; 
}

C++ :

#include<iostream>
#include<cstdio>
using namespace std;
int gbs(int a,int b)
{
	int r,s=a*b;
	if(a>b)
	{
		r=a%b;
		while(r!=0)
		{
			a=b;
			b=r;
			r=a%b;
		}
		return b;
	}
	else
	{
		r=b%a;
		while(r!=0)
		{
			b=a;
			a=r;
			r=b%a;
		}
		return a;
	}
}
int main()
{
	int x,y;
	scanf("%d,%d",&x,&y);
	gbs(x,y);
	cout<<gbs(x,y);
	return 0;
}