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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] strArray = br.readLine().split(" ");
		int a = Integer.parseInt(strArray[0]);
		int b = Integer.parseInt(strArray[1]);
		System.out.println(getGCD(a, b));

	}

	public static int getGCD(int a, int b) {
		if (a == b) return a;
		else if (a < b) {
			return getGCD(a, b - a);
		}
		else return getGCD(a - b, a);
	}
}