#include <bits/stdc++.h>
#define ll long long
#define rep(i,m,n) for(int i=(m); i<=(n); i++)
#define reb(i,m,n) for(int i=(m); i>=(n); i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define MP make_pair
#define fs first
#define se second
#define bit(msk, i) ((msk >> i) & 1)
#define iter(id, v) for(auto id : v)
#define pb push_back
#define SZ(v) (int)v.size()
#define ALL(v) v.begin(),v.end()
using namespace std;
mt19937_64 rd(chrono :: steady_clock :: now ().time_since_epoch().count());
ll Rand (ll l, ll r) { return uniform_int_distribution<ll> (l, r) (rd); }
const int N = 5e5 + 7;
const int Mod = 1e9 + 7;
const int INF = 1e9 + 7;
const ll BASE = 137;
int n;
int a[N];
vector<int> pos[N];
pii pre[N], suf[N];
struct Node {
int premn, sufmn, premx, sufmx, sum;
};
struct Segment_Tree {
int m;
Node st[N << 2] ;
void init (int n) {
m = n;
}
Node mer (Node lf, Node rt) {
Node cur;
cur.sum = lf.sum + rt.sum;
cur.premn = min(lf.premn, lf.sum + rt.premn);
cur.premx = max(lf.premx, lf.sum + rt.premx);
cur.sufmn = min(rt.sufmn, rt.sum + lf.sufmn);
cur.sufmx = max(rt.sufmx, rt.sum + lf.sufmx);
return cur;
}
void update (int id, int l, int r, int pos, int val) {
if (l > pos || r < pos)
return;
if (l == r) {
st[id].sum = val;
st[id].premn = st[id].sufmn = min(val, 0);
st[id].premx = st[id].sufmx = max(val, 0);
return;
}
int mid = l + r >> 1;
update (id << 1, l, mid, pos, val);
update (id << 1 | 1, mid + 1, r, pos, val);
st[id] = mer(st[id << 1], st[id << 1 | 1]);
}
Node get (int id, int l, int r, int u, int v) {
if (l > v || r < u || u > v) return {0, 0, 0, 0, 0};
if (l >= u && r <= v) return st[id];
int mid = l + r >> 1;
return mer (get (id << 1, l, mid, u, v), get (id << 1 | 1, mid + 1, r, u, v));
}
void update (int pos, int val) {
update (1, 1, m, pos, val);
}
Node get (int u, int v) {
return get (1, 1, m, u, v);
}
}ST;
bool check (pii cur, ll K) {
if (cur.se < 0) cur = MP(-cur.se, -cur.fs);
if (cur.se <= K) return 1;
if (cur.fs <= K) return 1;
return 0;
}
pii mer (pii A, pii B) {
return MP(min(A.fs, B.fs), max(A.se, B.se));
}
int sequence (int _n, vector<int> _a) {
//void solution () {
// cin >> n;
// rep (i, 1, n) {
// cin >> a[i];
// }
n = _n;
rep (i, 1, n) a[i] = _a[i - 1];
rep (i, 1, n) {
pos[a[i]].pb(i);
}
ST.init(n);
rep (i, 1, n) ST.update (i, 1);
int res = 1;
rep (x, 1, n) {
vector<int> &curp = pos[x];
iter (&id, curp) ST.update(id, 0);
// cout << x<<":\n";
pii seg2 = MP(0, 0);
int m = SZ(curp);
reb (i, m - 1, 0) {
int nxt = i < m - 1 ? curp[i + 1] - 1 : n;
int added = ST.get(curp[i] + 1, nxt).sum;
int delta = i == m - 1 ? 0 : 1;
seg2 = MP(seg2.fs + added - delta, seg2.se + added + delta);
Node get = ST.get(curp[i] + 1, nxt);
pii cur = MP(get.premn, get.premx);
seg2 = mer(seg2, cur);
suf[i] = seg2;
}
pii seg1 = MP(0, 0);
rep (i, 0, m - 1) {
int prv = i > 0 ? curp[i - 1] + 1 : 1;
int added = ST.get (prv, curp[i] - 1).sum;
int delta = i == 0 ? 0 : 1;
seg1 = MP(seg1.fs + added - delta, seg1.se + added + delta);
Node get = ST.get (prv, curp[i] - 1);
// if (x == 1 && i == 0) cout << get.premn<<",<"<<get.premx<<"\n";
pii cur = MP(get.sufmn, get.sufmx);
seg1 = mer(seg1, cur);
pre[i] = seg1;
}
rep (i, 0, m - 1) {
while (i + res < m) {
int added = ST.get(curp[i] + 1, curp[i + res] - 1).sum;
pii cur = MP(pre[i].fs + added + suf[i + res].fs, pre[i].se + added + suf[i + res].se);
if (check(cur, res + 1)) ++res;
else {
// cout << i <<" "<<res<<" "<<cur.fs<<" "<<cur.se<<"\n";
break;
}
}
}
iter (&id, curp) ST.update(id, -1);
}
// cout << res <<"\n";
return res;
}
//
//#define file(name) freopen(name".inp","r",stdin); \
//freopen(name".out","w",stdout);
//int main () {
// file("c");
// ios_base :: sync_with_stdio(false); cin.tie(0); cout.tie(0);
// int num_Test = 1;
//// cin >> num_Test;
// while (num_Test--)
// solution();
//}
/*
no bug challenge +2
2 + 8 * 2 - 9
*/
