D - Deletable Subarrays

An array $B$ is called *deletable* if and only if it can be made completely empty by the use of the following operation several times: - Choose $1 \le i < |B|$ such that $B_i = B_{i + 1}$, and remove both $B_i$ and $B_{i + 1}$ from the array. Given an array $A$ of length $N$, count the number of *deletable* subarrays. Formally, compute the following sum: $$ \sum_{L = 1}^{N} \sum_{R = L}^{N} [\t