#!/usr/local/bin/python2
import sys
sys.setrecursionlimit(3000)

def ack1(M, N):
   return (N + 1) if M == 0 else (
      ack1(M-1, 1) if N == 0 else ack1(M-1, ack1(M, N-1)))

def ack2(M, N):
    if M == 0:
        return N + 1
    elif N == 0:
        return ack2(M - 1, 1)
    else:
        return ack2(M - 1, ack2(M, N - 1))

print ack1(0,0) # 1
print ack1(3,5) # 253
print ack2(0,0) # 1
print ack2(3,5) # 253
print ack1(4,0) # 13
# print ack1(4,1) # maximum recursion depth exceeded
print ack2(4,0) # 13
# print ack2(4,1) # maximum recursion depth exceeded