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

$line = fgets(STDIN);

$lines = explode(" ", $line);

$lines[0] = trim($lines[0]);
$lines[1] = trim($lines[1]);

while(True){
    if($lines[0] < $lines[1]){
        $tmp = $lines[0];
        $lines[0] = $lines[1];
        $lines[1] = $tmp;
    }
    
    if($lines[0] % $lines[1] == 0){
        echo $lines[1];
        break;
    }else{
        $lines[0] = $lines[0] % $lines[1];
    }
}

?>