B. Make It Ugly

Let's call an array 𝑎 beautiful if you can make all its elements the same by using the following operation an arbitrary number of times (possibly, zero):

• choose an index 𝑖 (2≤𝑖≤|𝑎|−1) such that 𝑎𝑖−1=𝑎𝑖+1, and replace 𝑎𝑖 with 𝑎𝑖−1.

You are given a beautiful array 𝑎1,𝑎2,…,𝑎𝑛. What is the minimum number of elements you have to remove from it in order for it to stop being beautiful? Swapping elements is prohibited. If it is impossible to do so, then output -1.