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: WA: Presentation Error)

<?php
    // ??\???????????????
    $num = fgets(STDIN);
    $outnum = explode(" ", $num);
    $a = $outnum[0];
    $b = $outnum[1];
    $r = 1;
    while ($r != 0) {
        $r = $a % $b;
        if ($r == 0) echo $b;
        $a = $b;
        $b = $r;
    }
?>