Problem Statement

You are given $a sequence a = (a_1, \dots, a_N)$ of length N consisting of integers between 1 and N.
Find the number of pairs of integers i, j that satisfy all of the following conditions:

• $1 \leq i \lt j \leq N$
• $\min(a_i, a_j) = i$
• $\max(a_i, a_j) = j$

Input

Input is given from Standard Input in the following format:
N
$a_1 \ldots a_N$

Output

Print the answer.

Constraints

• $2 \leq N \leq 5 \times 10^5$
• $1 \leq a_i \leq N$ $, (1 \leq i \leq N)$
• All values in input are integers.

Sample Input 1

4
1 3 2 4

Sample Output 1

2

(i, j) = (1, 4), (2, 3) satisfy the conditions.

Sample Input 2

10
5 8 2 2 1 6 7 2 9 10

Sample Output 2

8

见题面 Input 部分

见题面 Output 部分