SP7741 BOI7SEQ - Sequence

We are given a sequence a1 , ..., an . We can manipulate this sequence using the operation reduce(i), which replaces elements ai and ai+1 with a single element max(ai , ai+1 ), resulting in a new shorter sequence. The cost of this operation is max(ai , ai+1 ). After n−1 operations reduce, we obtain a sequence of length 1. Our task is to compute the cost of the optimal reducing scheme, i.e. the sequence of reduce operations with minimal cost leading to a sequence of length 1.

The first line contains n (1

In the first and only line of the output print the minimal cost of reducing the sequence to a single element.