def fibo(f_0,f_1,n)
	case n
	when 0
		return f_0
	when 1
		return f_1
	else
		f = 0
		(n - 1).times{
			f = f_0 ^ f_1
			f_0 = f_1
			f_1 = f
		}
		return f
	end
end

f_0,f_1,n = gets.chomp.split(" ").map(&:to_i)
puts fibo(f_0,f_1,n)