using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("GCD of two numbers is: "+ GCD(21,35));

    }

    public static int GCD(int a,int b){

        int x,y;

        if(a>b){

            y=a;

            x=b;

        }

        else{

            x=a;

            y=b;

        }

        if(y%x ==0)

            return x;

        return GCD(y%x,x);

    }

}