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

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