Story

"Today I'm fresh from possessing someone, piping hot!"

Problem Statement

There are $N$ yokai. When $P_i\neq 0$, yokai $i(1\leq i\leq N)$ uses yokai $P_i$ as a shikigami; when $P_i=0$, it has no shikigami.

Find how many yokai are a shikigami of a shikigami.

Here, yokai $i$ is called a shikigami of a shikigami if the following condition is satisfied.

• There exists a pair $(p, q)$ satisfying all of the following:
  • $1\leq p, q\leq N$ and $p\neq q$
  • Yokai $p$ uses yokai $i$ as a shikigami
  • Yokai $q$ uses yokai $p$ as a shikigami
  • There is no yokai that uses yokai $q$ as a shikigami

Input

$N$
$P_1\ P_2 \cdots\ P_N$

• $1\leq N\leq 10^5$
• $0\leq P_i \leq N$
• $P_i\neq i$
• All inputs are integers

Output

Let $n$ be the number of yokai satisfying the condition, and output it on $1$ line in the following format.

$n$

Print a newline at the end.

Sample

3
2 3 0

1

2
0 1

0

6
2 3 0 5 6 0

2