Python Reduce Steps Challenge

reduce_steps.py

def calc_steps(num):
    count = 0
    while num > 1:
        if num % 2 == 0:  # bitmask: *0
            num = num // 2
        elif num == 3 or num % 4 == 1:  # bitmask: 01
            num -= 1
        else:  # bitmask: 11
            num += 1
        count += 1
    return count


def solution(s):
    return calc_steps(int(s))


print solution('199999999999999999')  # 73
print solution('15')  # 5
print solution('4')  # 2