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 Ruby (judge verdict: Accepted)

def _gcd(a, b)
    return a if b == 0
    gcd(b, a % b)
end

def gcd(a, b)
    if a < b
        tmp = a
        a = b
        b = tmp
    end
    
    _gcd(a, b)
end

a, b = gets.chomp.split.map(&:to_i)

puts gcd(a, b)