The challenge provides a domain and port to connect to with `nc`. Upon connection, you are prompted to solve some simple math problems, but the timeout is too quick to reasonably do so manually. I wrote a script to evaluate each of the provided expressions.
```python#!/usr/bin/env python3from pwn import *
# the connection is terminated before a final newline, this prints the buffer contentscontext.log_level = "debug"
conn = remote("calculator.ctf.cert.unlp.edu.ar", 15002)
conn.recvuntil(b":\n")
while True:    line = conn.recvline().strip()
    try:        result = str(eval(line)).encode("utf-8")    except Exception:        print("COMPLETE")        while(True):            print(line)            line = conn.recvline()
    conn.sendline(result)
    print(conn.recvline())```
I didn't write down the flag :p