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)

class String
  def to_ia
    self.split(/\s+/).map {|s| s.to_i}
  end
end

def gcd(xy)
  xy.sort!
  x = xy[0]
  y = xy[1]
  r = y % x
  if r > 0
    gcd([x, y % x].sort)
  else
    x
  end
end

puts gcd(STDIN.readline.to_ia)