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 PHP (judge verdict: Accepted)

<?php

fscanf(STDIN, '%d %d', $a, $b);
if ($a < $b) {
    list($a, $b) = array($b, $a);
}

while ($b > 0) {
    list($a, $b) = array($b, $a % $b);
}

echo $a, PHP_EOL;