using System;
class CalculateGCD
{
    static void Main()
    {
        int a, b;
        Console.Write("Enter value of \"a\": ");
        while (!int.TryParse(Console.ReadLine(), out a))
        {
            Console.WriteLine("Invalid input.Try again.");
            Console.Write("Enter value of \"a\": ");
        }
        Console.Write("Enter value of \"b\": ");
        while (!int.TryParse(Console.ReadLine(), out b))
        {
            Console.WriteLine("Invalid input.Try again.");
            Console.Write("Enter value of \"b\": ");
        }

        while (b!=0)
        {
            int temp = b;
            b = a % b;
            a = temp;
        }
        Console.WriteLine(a);
    }
}