#include <bits/stdc++.h>
using namespace std;
#define A first
#define B second
#define MP make_pair
#define ms(a, x) memset(a, x, sizeof(a))
#define boost() ios_base::sync_with_stdio(false); cin.tie(0)
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef pair<long double, long double> pld;
const int INF = 0x3f3f3f3f;
const ll LLINF = 0x3f3f3f3f3f3f3f3f;
const double PI = acos(-1);
const int mxN=2e4+5;
vector <int> a(mxN);
int main(){
int n;
cin >> n;
for(int i=0; i<n; i++)
cin >> a[i];
int ans1=0;
for(int i=0; i<n; i++){
int before=a[i];
for(int j=-1; j<n; j++){
a[i]=j;
bool path1[mxN]={};
int lnode=0, ans=0;
while(lnode != -1 && !path1[lnode]){
path1[lnode]=1;
ans++;
lnode = a[lnode];
}
if(lnode == -1)
ans1 = max(ans, ans1);
}
a[i] = before;
}
cout << ans1;
}
