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 geta(n=0)
  return $stdin.gets.to_i if n==0
  ar = []
  n.times do 
    ar << $stdin.gets.chomp.split
  end
  return ar.flatten(1) if n<=1
  return ar
end

@ar = geta(1).map(&:to_i)
y,x = @ar.sort

rems = [y]
while (rem=x%y)>0
  rems << rem
  x = y
  y = rem
end

p rems.min