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.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main{

	public static void main(String[] args) throws NumberFormatException, IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		//BufferedReader br = new BufferedReader(new FileReader("sample.txt"));
		StringTokenizer stk=new StringTokenizer(br.readLine());
		int a=Integer.parseInt(stk.nextToken());
		int b=Integer.parseInt((String)stk.nextElement());
		System.out.println(yakusuu(a,b));
	}
	static int yakusuu(int a,int b){
		if(a<b){int tmp=a;
			a=b;
			b=tmp;}
		while(a%b!=0){			
			int l=a%b;
			a=b;b=l;}
		return b;
	}

}