I don't know if it was intended or not but this can be done in one go .As we know that on sending our input we get the output xored with the flag.

```python
from pwn import *

charset="*"*26

r=remote("142.93.113.55",31087)
print(r.recv())
r.sendline("start")
r.recv()
r.sendline(charset)

resp= r.recv()
print(''.join([chr(ord(i)^ord('*')) for i in resp]))

r.close()
```

The flag is F#{us1ng-X0r-is-ROx-4-l0t}