Fixed Points

题意翻译

给你一个 0 ~ n-1 的全排列，可以交换两个数的位置一次，问最多能有多少个数与自己所在的位置对应

题目描述

A permutation of length $ n $ is an integer sequence such that each integer from 0 to $ (n-1) $ appears exactly once in it. For example, sequence $ [0,2,1] $ is a permutation of length 3 while both $ [0,2,2] $ and $ [1,2,3] $ are not. A fixed point of a function is a point that is mapped to itself by the function. A permutation can be regarded as a bijective function. We'll get a definition of a fixed point in a permutation. An integer $ i $ is a fixed point of permutation $ a_{0},a_{1},...,a_{n-1} $ if and only if $ a_{i}=i $ . For example, permutation $ [0,2,1] $ has $ 1 $ fixed point and permutation $ [0,1,2] $ has $ 3 $ fixed points. You are given permutation $ a $ . You are allowed to swap two elements of the permutation at most once. Your task is to maximize the number of fixed points in the resulting permutation. Note that you are allowed to make at most one swap operation.

输入输出格式

输入格式

The first line contains a single integer $ n $ $ (1<=n<=10^{5}) $ . The second line contains $ n $ integers $ a_{0},a_{1},...,a_{n-1} $ — the given permutation.

输出格式

Print a single integer — the maximum possible number of fixed points in the permutation after at most one swap operation.

输入输出样例

输入样例 #1

5
0 1 3 4 2

输出样例 #1

3