题目描述
There are N people, conveniently numbered 1 through N. They were standing in a row yesterday, but now they are unsure of the order in which they were standing. However, each person remembered the following fact: the absolute difference of the number of the people who were standing to the left of that person, and the number of the people who were standing to the right of that person. According to their reports, the difference above for person i is A_i.
Based on these reports, find the number of the possible orders in which they were standing. Since it can be extremely large, print the answer modulo 10^9+7. Note that the reports may be incorrect and thus there may be no consistent order. In such a case, print 0.
Constraints
- 1≦N≦10^5
- 0≦A_i≦N-1
Input
The input is given from Standard Input in the following format:
N
A_1 A_2 ... A_N
Output
Print the number of the possible orders in which they were standing, modulo 10^9+7.
Examples
Input
5
2 4 4 0 2
Output
4
Input
7
6 4 0 2 4 0 2
Output
0
Input
8
7 5 1 1 7 3 5 3
Output
16
输入格式
见题面
输出格式
见题面