#include <bits/stdc++.h>
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define vi vector<int>
#define vl vector<ll>
#define mp make_pair
#define pb push_back
using namespace std;
const int mxn = 1e5;
int n, nxt[mxn], arr[mxn], tree[mxn*4];
void update(int node, int l, int r, int pos, int value){
    if(l == r){
        tree[node] = value;
    }
    else{
        int mid = (l + r) / 2;
        if(pos <= mid)
            update(node * 2, l, mid, pos, value);
        else
            update(node * 2 + 1, mid + 1, r, pos, value);

        tree[node] = tree[node * 2] + tree[node * 2 + 1];
    }
}
int query(int node, int l, int r, int L, int R){
    if(l > R || r < L)
        return 0;
    if(L <= l && r <= R)
        return tree[node];

    int mid = (l + r) / 2;
    int left = query(node * 2, l, mid, L, R);
    int right = query(node * 2 + 1, mid + 1, r, L, R);
    return left + right;
}
int main(){
    cin>>n;
    for(int i = 0; i < n; i++){
        cin>>arr[i];
    }
    int lbl = 1;
    map<int,int> label;
    for(int i = 0; i < n; i++){
        if(label[arr[i]])
            continue;
        else{
            label[arr[i]] = lbl++;
        }
    }
    map<int,int> last;
    for(int i = 0; i < n; i++)
        nxt[i] = -1;
    for(int i = n - 1; i >= 0; i--){
        if(last[arr[i]]){
            nxt[i] = last[arr[i]];
            last[arr[i]] = i;
        }
        else{
            last[arr[i]] = i;
        }
    }
    int ans = 0;
    set<int> ones;
    for(int i = n - 1; i >= 0; i--){
        int l = i, r = nxt[i];
        if(nxt[i] == -1)
            continue;
        update(1, 0, n-1,nxt[i], 1);
        if(ones.find(nxt[i]+1) == ones.end());
            ones.insert(nxt[i]);
        if(nxt[nxt[i]] != -1){
            ones.erase(nxt[nxt[i]]);
            update(1, 0, n-1, nxt[nxt[i]], -1);
        }
        if(nxt[nxt[i]] != -1 && nxt[nxt[nxt[i]]] != -1){
            update(1, 0, n-1, nxt[nxt[nxt[i]]], 0);
        }
        for(int j : ones){
            if(j >= i)
                ans = max(ans, query(1, 0, n-1, i, j));
        }
    }
    cout<<ans<<endl;
}