Write a function solution that given an integer N, returns the maximum possible value obtained by inserting one '5' digit inside the decimal representation of integer N.

Examples: 1. Given N = 268, the function should return 5268.

2. Given N = 670, the function should return 6750.

3. Given N = 0, the function should return 50.

4. Given N = -999, the function should return -5999.

Assume that: N is an integer within the range [-8000..8000].

C++