# Shortest python3 code for: Find the difference between a number and a power of two not exceeding a given number

## Python 3, 39 bytes

print(int('0'+bin(int(input()))[3:],2))


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Subtracting the largest power of two less than a number is the same as removing the first 1 from its binary representation.

Unfortunately python rather mysteriously errors on trying to convert the empty binary string to an int so we need '0'+ if we want it to work on zero or one. If we relax the requirements to only require two or more then we can remove 4 bytes.

## Python 3, 35 bytes

print(int(bin(int(input()))[3:],2))


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## Python 3, 40 39 bytes (not counting the newline)

First I simplified $$\2^{a-3}\$$ to $$\\frac{2^a}8\$$, then I used the lower-precedence operators << and ^ so that // can be replaced by - (which saves a byte).

x=int(input())
print(1<<len(bin(x))-3^x)


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