cache = {}

def ack(m,n):
    if (m,n) in cache:
        return cache[(m,n)]
    elif m == 0:
        ans = n+1
    elif n == 0:
        ans = ack(m-1,1)
    else:
        ans = ack(m-1, ack(m, n-1))
    cache[(m,n)] = ans
    return ans

if __name__ == "__main__":
    for i in range(6):
        for j in range(6):
            try:
                print("ack(%d,%d) = %d" % (i,j, ack(i,j)))
            except RuntimeError:
                print("ack(%d,%d) = <StackOverflow>" % (i,j))