题目描述
Aoki loves numerical sequences and trees.
One day, Takahashi gave him an integer sequence of length N, a_1, a_2, ..., a_N, which made him want to construct a tree.
Aoki wants to construct a tree with N vertices numbered 1 through N, such that for each i = 1,2,...,N, the distance between vertex i and the farthest vertex from it is a_i, assuming that the length of each edge is 1.
Determine whether such a tree exists.
Constraints
- 2 ≦ N ≦ 100
- 1 ≦ a_i ≦ N-1
Input
The input is given from Standard Input in the following format:
N
a_1 a_2 ... a_N
Output
If there exists a tree that satisfies the condition, print Possible. Otherwise, print Impossible.
Examples
Input
5
3 2 2 3 3
Output
Possible
Input
3
1 1 2
Output
Impossible
Input
10
1 2 2 2 2 2 2 2 2 2
Output
Possible
Input
10
1 1 2 2 2 2 2 2 2 2
Output
Impossible
Input
6
1 1 1 1 1 5
Output
Impossible
Input
5
4 3 2 3 4
Output
Possible
输入格式
见题面
输出格式
见题面