Recursion test

"""
"""
def func_rec(M, N):
    """
    recursion func which describe function Anckerman
    M, N : input values in func
    """
    assert (M >= 0 and N >= 0), 'M and N is equal or greater than zero'
    if M == 0:
        return (N + 1)
    elif M > 0 and N == 0:
        return func_rec(M-1, 1)
    elif M > 0 and N > 0:
        return func_rec(M-1, func_rec(M, N-1))

def main_func():
    """
    main funct to entry recursion func
    """
    M = int(input('M_val -->: '))
    N = int(input('N_val -->: '))
    assert (M <= 3 and N <= 3), 'input M and N is equal or less than 3 due to complexity'
    res = func_rec(M, N)    # result of func
    print(res)

if __name__ == "__main__":
    main_func()