The main page looked like http://petushok.2018.ctf.kaspersky.com/?logo=petushok.pngThe picture name can be changed to http://petushok.2018.ctf.kaspersky.com/?logo=main.py. The main.py name was guessed. There is an import cococo, lets get it.http://petushok.2018.ctf.kaspersky.com/?logo=cococo.py.
We have check function there, the task is to find the check input which gives 1.
The solver:
```def check(value):    # a lot of code    return (a140574420399240, a140574420399456, ..., (a140574419586512 + 1), (a140574419608064 + 1))
def brute_from(n, condition_idx):    end_pos = (condition_idx + 104) % 137
    if condition_idx >= 300:        print("flag", hex(n))        exit()
    q = check(n)    if q[condition_idx % 137] == 1:        brute_from(n, condition_idx+1)
    n ^= 1 << end_pos    q = check(n)    if q[condition_idx % 137] == 1:        brute_from(n, condition_idx+1)
brute_from(0, 0)
```