def ack2(M, N):
   return (N + 1)   if M == 0 else (
          (N + 2)   if M == 1 else (
          (2*N + 3) if M == 2 else (
          (8*(2**N - 1) + 5) if M == 3 else (
          ack2(M-1, 1) if N == 0 else ack2(M-1, ack2(M, N-1))))))