This task was essentially the same as the previous one called hertz.

I used the same approach with two small differences :

1. I had to modify my script to handle capital letter
2. The ciphertext was considerably shorter and ended with
`nxugUAR{edyeaxadaxgt_uxnifke_qkf_agg_fqep_jeukedvgml}`. Knowing the flag
format, I guessed the initial substitutions for the letters `p`, `i`, `c`,
`o`, `t` and `f`.

Here's my updated script after those initial guesses :

```python
from string import ascii_lowercase
from collections import Counter
from colorama import Fore

with open('ciphertext', 'r') as f:
ciphertext = f.read()

# Get the letter frequency
charcount = Counter(c for c in ciphertext if c in ascii_lowercase)
total_chars = sum(charcount.values())
for char, count in charcount.items():
print(f'{char}: {(count*100)/total_chars}% ({count})')

# Reverse the substitutions
sub = {
'n': 'p',
'x': 'i',
'u': 'c',
'g': 'o',
'a': 't',
'r': 'f',
}
plaintext = ''
for char in ciphertext:
if char in sub:
char = char.replace(char, f'{Fore.GREEN}{sub[char]}{Fore.RESET}')
elif char.lower() in sub:
char = char.replace(char, f'{Fore.GREEN}{sub[char.lower()].upper()}{Fore.RESET}')
plaintext += char

print(plaintext)
```

_Note : this uses the third-party library
[colorama](https://github.com/tartley/colorama) for colored output._