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.*;
import java.util.*;

public class Main {

    private static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));    
    private static StringTokenizer st;

    public static void main ( String [] args ) throws IOException
    {
	new Main().cal();
    }

 
    private void cal() throws IOException 
    {
	st = new StringTokenizer(br.readLine());
	int a = Integer.parseInt(st.nextToken());
	int b = Integer.parseInt(st.nextToken());

	int x, y;
	if ( a > b ) {
	    x = a; y = b;
	} else {
	    x = b; y = a;
	}

	while( y > 0 ) {
	    int temp = x;
	    x = y;
	    y = temp % y;
	}

	System.out.println(x);

	
	

    }

}