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: Time Limit Exceeded)

def divisor(num)
  divisor = []
  f = 1.0
  while 1 < num / f
    divisor << num / f.to_i if num % f == 0
    f += 1
  end
  divisor + [1]
end

puts gets.split.map {|num| divisor(num.to_i)}.inject {|m, n| m & n}.max