#include<bits/stdc++.h>
using namespace std;
const int N = 1e6 + 10;
int n;
int a[N];
int belong[N];//第i个点属于第几个环
int cnt[N];//维护每一个环的个数
int idx;//到第几个环

void solve(){
    cin >> n;
    for(int i = 1; i <= n; i ++){
        cin >> a[i];
    }
    idx = 1;
    for(int i = 1; i <= n; i ++){
        if(!belong[i]){
            belong[i] = idx;
            cnt[idx] ++;
            int temp = i;
            while(a[temp] != i){
                temp = a[temp];
                belong[temp] = idx;
                cnt[idx] ++;
            }
            idx ++;
        }
    }
    if(idx == 2){
        cout << n;
        return ;
    }
    int ans = 0;
    for(int i = 2; i <= n; i ++){
        if(belong[i] != belong[i - 1]){
            ans = max(ans, cnt[belong[i]] + cnt[belong[i - 1]]);
        }
    }
    cout << ans;
}


int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    solve();
    return 0;
}