Game#3361
The game consists of levels. On the -th level, the player earns a_i points. The player begins at level and wins upon completing level . You can advance from level to level if level follows level (m < k), and the parity of a_k matches the parity of the distance between levels and . The cost of moving between these levels (points deducted) is equal to , which is the distance between them. Determine if the player can finish the game, and if so, calculate the maximum number of points they can achieve.
The first line of the input contains a single integer (1 \le N \le 10^5). The second line contains positive integers a_i, each not exceeding 10^9.
If the player can complete the game, output the maximum number of points they can score. If not, output "Impossible".
Example 1