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.io.File;
import java.util.Scanner;

public class Main {
	public static int gcd(int x, int y) {
		// x <= y?????????
		if (x == 0)
			return y;
		else
			return gcd(y % x, x);
	}
	
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		// Scanner sc = new Scanner(new File("test_1.txt"));
		// Scanner sc = new Scanner(new File("test_2.txt"));
		int x = sc.nextInt(), y = sc.nextInt();
		if (x <= y)
			System.out.println(gcd(x, y));
		else
			System.out.println(gcd(y, x));
	}
}