Write a python function to toggle bits of the number except the first and the last bit. https://www.geeksforgeeks.org/toggle-bits-number-expect-first-last-bits/
def set_middle_bits(n):  
    n |= n >> 1; 
    n |= n >> 2; 
    n |= n >> 4; 
    n |= n >> 8; 
    n |= n >> 16;  
    return (n >> 1) ^ 1
def toggle_middle_bits(n): 
    if (n == 1): 
        return 1
    return n ^ set_middle_bits(n) 