Minimum Grid Path

Let's say you are standing on the $$$XY$$$-plane at point $$$(0, 0)$$$ and you want to reach point $$$(n, n)$$$.

You can move only in two directions:

• to the right, i. e. horizontally and in the direction that increase your $$$x$$$ coordinate,
• or up, i. e. vertically and in the direction that increase your $$$y$$$ coordinate.

In other words, your path will have the following structure:

• initially, you choose to go to the right or up;
• then you go some positive integer distance in the chosen direction (distances can be chosen independently);
• after that you change your direction (from right to up, or from up to right) and repeat the process.

You don't like to change your direction too much, so you will make no more than $$$n - 1$$$ direction changes.

As a result, your path will be a polygonal chain from $$$(0, 0)$$$ to $$$(n, n)$$$, consisting of at most $$$n$$$ line segments where each segment has positive integer length and vertical and horizontal segments alternate.

Not all paths are equal. You have $$$n$$$ integers $$$c_1, c_2, \dots, c_n$$$ where $$$c_i$$$ is the cost of the $$$i$$$-th segment.

Using these costs we can define the cost of the path as the sum of lengths of the segments of this path multiplied by their cost, i. e. if the path consists of $$$k$$$ segments ($$$k \le n$$$), then the cost of the path is equal to $$$\sum\limits_{i=1}^{k}{c_i \cdot length_i}$$$ (segments are numbered from $$$1$$$ to $$$k$$$ in the order they are in the path).

Find the path of the minimum cost and print its cost.