# Time: O(N) where N is number of bits
class Solution:
    def bitwiseComplement(self, n: int) -> int:
        if n == 0:
            return 1
        
        cn, bit = n, 1
        
        while n > 0:
            # XOR 1 can be used to flip bit.
            # 0 XOR 1 = 1
            # 1 XOR 1 = 0
            cn = cn ^ bit
            
            bit = bit << 1
            n = n >> 1
        
        return cn