Given a positive integer 'n', the task is to find a prime number greater than or equal to 'n'.
If given 'n' is 10, then the closest prime number greater than 10 is 11 at a distance of 1. So 11 must be returned.
If the given 'n' is 17, then the closest prime number is itself at a distance of 0. So 17 must be returned.
The returned prime number must be greater than or equal to 'n'.