mod_fib.rb

def fib_mod(a,b,x,sequence = []) 
  if x == 1
    result = a
  elsif x == 2
    result = b 
  else
    result1 = sequence[x - 1] ||= fib_mod(a,b,x - 1, sequence)
    result2 = sequence[x - 2] ||= fib_mod(a,b,x - 2, sequence)
    result = result1**2 + result2
  end
  sequence[x] = result
  return result
end

args = gets
puts fib_mod(*args.split(' ').map{|x| x.to_i})