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.

Constraints

• $0 \leq A, B, C \leq 10^{18}$

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.