Problem Statement

Three non-negative integers A, B, and C are written on a blackboard.
You can perform the following two operations any number of times in any order.

• Subtract 1 from two of the written integers of your choice.
• Subtract 1 from all of the written integers.

Your objective is to make all the numbers on the blackboard 0.
Determine whether it is achievable. If it is, find the minimum number of times you need to perform an operation to achieve it.

Input

Input is given from Standard Input in the following format:
A B C

Output

If the objective is unachievable, print -1. If it is achievable, print the minimum number of times you need to perform an operation to achieve it.

Constraints

• $0 \leq A, B, C \leq 10^{18}$

Sample Input 1

2 2 3

Sample Output 1

3

Here is one way to make all the numbers 0.

• Subtract 1 from A and C. Now the numbers are 1, 2, 2.
• Subtract 1 from B and C. Now the numbers are 1, 1, 1.
• Subtract 1 from all the numbers. Now the numbers are 0, 0, 0.

Sample Input 2

0 0 1

Sample Output 2

-1

Sample Input 3

0 0 0

Sample Output 3

0

见题面 Input 部分

见题面 Output 部分