def sat(d: int):
"""
Find a number bigger than n whose decimal representation has k 4's and 7's where k's decimal representation
consists only of 4's and 7's
Inspired by [Codeforces Problem 110 A](https://codeforces.com/problemset/problem/110/A)
"""
return d > 123456789 and set(str(str(d).count("4") + str(d).count("7"))) <= {"4", "7"}
Solvers, post your solutions in the comments using the following formatting:
<details><summary>Reveal solution</summary>
```python
def sol():
return "world" # replace with your solution
Solvers, post your solutions in the comments using the following formatting: