fibomod.rb

#!/usr/bin/env ruby

def fiboMod (t1, t2, n)
    n = n-1
    if n == 1
        return t2
    else
        return fiboMod(t2, t2**2 + t1, n)
    end
end

t1, t2, n = gets.strip.split.map {|i| i.to_i }

puts fiboMod(t1, t2, n)