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

function input_array() {
    return explode(' ', trim(fgets(STDIN)));
}

function gcd($x, $y) {
    if ($x < $y) {
        list($x, $y) = [$y, $x];
    }
    while ($y !== 0) {
        list($x, $y) = [$y, $x % $y];
    }
    return $x;
}

list($x, $y) = array_map(function($numeric_string) {
    return (int)$numeric_string;
}, input_array());

echo gcd($x, $y) . "\n";