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 int gcd(int first, int second) {
	    if(second == 0) {
	        return first;
	    }
		return gcd(second, first % second);
	}

	public static void main(String[] args) {
		// user input line here
		Scanner sc = new Scanner(System.in);
		// pull numbers
		int first = sc.nextInt();
		int second = sc.nextInt();
		// print the result of gcd() with inputted numbers
		int exp = (int) Math.pow(10, 9);
		if(first>=1 && second <= exp) {
			System.out.println(gcd(first, second));
		}
	}

}