Recon
This is the correct output of the binary that we want to each
Looks like it has a check for the string length of the input first
There is this function called check
So it runs the check function after user input, and depending on its result it puts success or fail
Decompilation
Check()
First, the flag must have a length of 26 characters
Lets use a dummy flag: picoCTF{aaaaaaaaaaaaaaaaa}
we know that it is reading character by character