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(x, y)
  if y > x
    tmp = x
    x = y
    y = tmp
  end
  return x if y == 0
  gcd(y, x % y)
end
     
x,y=gets.split.map &:to_i
#p gcd(x, y)

if y > x
  tmp = x
  x = y
  y = tmp
end
while y > 0
  r = x % y
  x = y
  y = r
end
p x