Given a Binary Number B, find its decimal equivalent.
 

Example 1:

Input: B = 10001000
Output: 136

Example 2:

Input: B = 101100
Output: 44

Your Task:
You don't need to read or print anything. Your task is to complete the function binary_to_decimal() which takes the binary number as string input parameter and returns its decimal equivalent.
 

Expected Time Complexity: O(K * Log(K)) where K is number of bits in binary number.
Expected Space Complexity: O(1)
 

Constraints:
1 <= number of bits in binary number  <= 16