MaximumMoves | Topcoder Archive

Problem Statement

You are given two nonnegative integers P and Q. Your task is to make the integers equal in as many steps as possible. In each step you can do one of two things:

Add any prime number to P.
Subtract any prime number from Q.

If it's not possible to make P and Q equal, return -1. Otherwise, return a nonnegative integer: the maximum (not minimum!) number of steps you can make.

Definition

Class:: MaximumMoves
Method:: getMaximumMoves
Parameters:: long, long
Returns:: long
Method signature:: long getMaximumMoves(long P, long Q)
(be sure your method is public)

Notes

Primes are positive integers with exactly two positive integer divisors. The smallest few primes are 2, 3, 5, 7, 11, 13, ...
In particular, the numbers 0 and 1 are not prime numbers.

Constraints

P will be between 0 and 10^18, inclusive.
Q will be between 0 and 10^18, inclusive.

Examples

```
5
```
```
9
```
```
Returns: 2
```
In one optimal solution we first subtract 2 from Q and then add 2 to P. After these two steps both numbers are equal (both are 7).
```
5
```
```
10
```
```
Returns: 2
```
In one optimal solution we first subtract 2 from Q and then add 3 to P. After these two steps both numbers are equal (both are 8).
```
5
```
```
6
```
```
Returns: -1
```
There's no way to make these P and Q equal.
```
10
```
```
2
```
```
Returns: -1
```

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