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(a, b)
  if a > b then
    a, b = b, a
  end
  
  while a % b != 0 do
    r = a % b
    a = b
    b = r
  end
  b
end

def main()
  a, b = gets.split.map{|x| x.to_i}
  puts gcd(a, b)
end

main