The program works as follow:

• For every number n, n and n - 1 are converted to base 3
• The program compare the digits, the number of differences is added to total

By observation, we can see that:

• For every number n, most of the time the difference is 1
• If n is divisible by 3, the difference is 2
• If n is divisible by 3, the difference is 3, and so on

Final program:

def count3(n):
    sum = 0
    while (n > 0):
        sum += n
        n //= 3
    return sum

print(count3(523693181734689806809285195318))

Flag: csictf{785539772602034710213927792950}