#include<vector>
#include<iostream>
#include<map>
#include<queue>

using namespace std;
using ll = long long ;

priority_queue<int> mxheap;
priority_queue<int,vector<int>,greater<int>> mnheap;

const int N =1e6+9;
int n;
int a[N];//存储原数组
int c[N];//存储联通
int p[N];//存储数量

void solve(){
	cin>>n;
	for(int i=1; i<=n;i++) cin>>a[i];
	
	int id = 0;
	
	for(int i=1; i<=n;i++){
		if(!c[i]) id++;
		
		
		int curr = i ;
		int count = 0 ;
		while(!c[curr]){
			c[curr] = id;
			count++;
			curr = a[curr];
			
			p[id] = count;
		}
		
	}
	
	int mx =0 ;
	for(int i=1; i<=id ; i++){
		mx = max(mx , p[i]);
	}
	
	for(int i=1; i<=n;i++){
		int left = c[i];
		int right = c[i+1];
		
		if(left != right){
			mx = max(mx , p[left] + p[right]);
		}
	}
	
	
	cout<<mx<<endl;
}

int main(){
	ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	int t_ = 1;
	while(t_--) solve();
	
	
	return 0;
}