1def function_that_says_ni(*args, **kwargs):
 2    valid_keys = ("bush", "shrub", "храст") # added tuple with valid keywords
 3    cost = 0.0
 4    kwargs_names = []
 5    unique_letters = set()
 6
 7    for arg in args:
 8        if type(arg) == dict:
 9            name = arg.get("name")
10            if name is not None:
11                if type(name) == str:
12                    name = name.lower()
13                    if name in valid_keys:
14                        # corrected without additional if-check
15                        cost += arg.get("cost", 0)
16
17    for key, value in kwargs.items():
18        if type(value) == dict:
19            name = value.get("name")
20            if name is not None:
21                if type(name) == str:
22                    name = name.lower()
23                    if name in valid_keys:
24                        kwargs_names.append(key)
25                        # corrected without additional if-check
26                        cost += value.get("cost", 0)
27
28    for name in kwargs_names:
29        # corrected using built-in method
30        unique_letters.update(name)
31
32    unique_letters_count = len(unique_letters)
33    whole_part = int(cost)
34
35    if cost <= 42.0 and whole_part > 0:
36        if unique_letters_count % whole_part == 0:
37            # corrected return
38            return f"{cost:.2f}лв"
39
40    return "Ni!"