Problem:
Greatest Common Divisor

Write a program which finds the greatest common divisor of two natural numbers a and b

Input

a and b are given in a line sparated by a single space.

Output

Output the greatest common divisor of a and b.

Constrants

1 ≤ a, b ≤ 109

Hint

You can use the following observation:

For integers x and y, if x ≥ y, then gcd(x, y) = gcd(y, x%y)

Sample Input 1

54 20

Sample Output 1

2

Sample Input 2

147 105

Sample Output 2

21

Solution in JAVA (judge verdict: Accepted)

import java.util.Scanner;

public class Main
{
	public static void main(String args[])
	{
		Scanner input = new Scanner(System.in);
		int a = input.nextInt();
		int b = input.nextInt();
		System.out.println(gcd(a, b));
	}

	public static int gcd(int a, int b)
	{
		if( a%b == 0 )
			return b;
		else
			return gcd(b, a%b);
	}
}