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)

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

if a < b
  x = b
  b = a
  a = x
end

while b != 0 && b <= a
  mod = a % b
  a = b
  b = mod
end

puts a