c++ map large numeric string to numeric string ranges

I have to write a C++ function where the input is a 12 digit numeric string. I have to find the range which is also stored in string arrays.

For Example,

Range array [10]:

1 - 111115555522 - 111225555521

2 - 111225555522 - 111335555521

3 - 111335555522 - 111445555521

4 - 111445555522 - 111555555521

5 - 111555555522 - 111665555521

6 - 111665555522 - 111775555521

7 - 111775555522 - 111885555521

8 - 111885555522 - 111995555521

9 - 111995555522 - 112005555521

10- 112005555522 - 113005555521

Input - 111555512440

Output - the number belongs to range - 5

I have used "long long" data type for numerical ranges and the input as well and accomplished it. But since I have to also maintain performance, can somebody give me a better idea to make it such that input value remains string as well as the ranges will also remain in string?

P.S.: I am fine with the use of "char" pointers instead of std::string.