#include<bits/stdc++.h>
#define fi first
#define se second
#define endl "\n"
#define ii pair<int, int>
using namespace std;
const int N = 5e5 + 10;
vector<int> pos[N];
int L[N], R[N];
int minx[N << 2], maxx[N << 2], lazy[N << 2];
void push(int s, int l, int r) {
if (!lazy[s]) return;
minx[s] += lazy[s];
maxx[s] += lazy[s];
if (l != r) {
lazy[s << 1] += lazy[s];
lazy[s << 1 | 1] += lazy[s];
}
lazy[s] = 0;
}
void up(int s, int l, int r, int from, int to, int val) {
push(s, l, r);
if (l > to || r < from) return;
if (from <= l && r <= to) {
lazy[s] = val;
push(s, l, r);
return;
}
int mid = l + r >> 1;
up(s << 1, l, mid, from, to, val);
up(s << 1 | 1, mid + 1, r, from, to, val);
minx[s] = min(minx[s << 1], minx[s << 1 | 1]);
maxx[s] = max(maxx[s << 1], maxx[s << 1 | 1]);
}
int get_min(int s, int l, int r, int from, int to) {
push(s, l, r);
if (l > to || r < from) return 1e9;
if (from <= l && r <= to) return minx[s];
int mid = l + r >> 1;
return min(get_min(s << 1, l, mid, from, to), get_min(s << 1 | 1, mid + 1, r, from, to));
}
int get_max(int s, int l, int r, int from, int to) {
push(s, l, r);
if (l > to || r < from) return -1e9;
if (from <= l && r <= to) return maxx[s];
int mid = l + r >> 1;
return max(get_max(s << 1, l, mid, from, to), get_max(s << 1 | 1, mid + 1, r, from, to));
}
int sequence(int n, vector<int> a) {
int ans = 1;
a.insert(a.begin(), 0);
for(int i = 1; i <= n; i++) pos[a[i]].push_back(i);
for(int i = 1; i <= n; i++) up(1, 0, n, i, i, -i);
for(int val = 1; val <= n; val++) {
pos[val].push_back(n + 1);
int pre = 0;
for(int i = 0; i + 1 < pos[val].size(); i++) {
int cur = pos[val][i];
L[i] = get_min(1, 0, n, pre, cur - 1);
R[i] = get_max(1, 0, n, pre, cur - 1);
int from = get_min(1, 0, n, cur, pos[val][i + 1] - 1);
int to = get_max(1, 0, n, cur, pos[val][i + 1] - 1);
// cout << cur << " " << pos[val][i + 1] - 1 << endl;
for(int j = i - 1; j >= 0; j--) {
// cout << L[j] << " " << R[j] << " " << from << " " << to << " " << j << " " << i << " " << to - L[j] + (i - j + 1) * 2 << endl;
// cout << (L[j] > to && to - L[j] + (i - j + 1) * 2 >= 0) << endl;
if (max(L[j], from) <= min(R[j], to)) ans = max(ans, i - j + 1);
else if (L[j] > to && to - L[j] + (i - j + 1) * 2 >= 0) ans = max(ans, i - j + 1);
}
}
for(int &j : pos[val]) up(1, 0, n, j, n, 2);
}
return ans;
}
#ifdef ngu
int main() {
freopen ("task.inp", "r", stdin);
freopen ("task.out", "w", stdout);
// int n; cin >> n;
// vector<int> a(n);
// for(int i = 0; i < n; i++) cin >> a[i];
// cout << sequence(n, a);
// cout << sequence(7, {1, 2, 3, 1, 2, 1, 3});
// cout << sequence(9, {1, 1, 2, 3, 4, 3, 2, 1, 1});
cout << sequence(14, {2, 6, 2, 5, 3, 4, 2, 1, 4, 3, 5, 6, 3, 2});
}
#endif // ngu
