#include <bits/stdc++.h>
using namespace std;
#ifndef LOCAL
#include "sequence.h"
#endif
const int N = 500'000 + 10;
int n;
int a[N];
vector<int> pos[N];
namespace IT {
struct Node {
int mi, ma;
Node() : mi(1'000'000), ma(-1'000'000) {}
Node(int mi, int ma) : mi(mi), ma(ma) {}
} f[N << 2];
int lazy[N << 2];
inline Node merge(const Node& lt, const Node& rt) {
return Node(min(lt.mi, rt.mi), max(lt.ma, rt.ma));
}
void build(int s, int l, int r) {
f[s] = Node(0, 0);
lazy[s] = 0;
if (l == r) return;
int mid = (l + r) >> 1;
build(s << 1, l, mid); build(s << 1 | 1, mid + 1, r);
}
void push(int s) {
if (!lazy[s]) return;
f[s << 1].mi += lazy[s]; f[s << 1 | 1].mi += lazy[s];
f[s << 1].ma += lazy[s]; f[s << 1 | 1].ma += lazy[s];
lazy[s << 1] += lazy[s]; lazy[s << 1 | 1] += lazy[s];
lazy[s] = 0;
}
void update(int s, int l, int r, int u, int v, int x) {
if (v < l || u > r) return;
if (u <= l && r <= v) {
f[s].mi += x;
f[s].ma += x;
lazy[s] += x;
return;
}
push(s);
int mid = (l + r) >> 1;
update(s << 1, l, mid, u, v, x); update(s << 1 | 1, mid + 1, r, u, v, x);
f[s] = merge(f[s << 1], f[s << 1 | 1]);
}
Node query(int s, int l, int r, int u, int v) {
if (v < l || u > r) return Node();
if (u <= l && r <= v) return f[s];
int mid = (l + r) >> 1;
return merge(query(s << 1, l, mid, u, v), query(s << 1 | 1, mid + 1, r, u, v));
}
}
IT::Node saveL[N], saveR[N];
int sequence(int inN, std::vector<int> inA) {
{ // input
n = inN;
for (int i = 1; i <= n; ++i) a[i] = inA[i - 1];
}
for (int i = 1; i <= n; ++i) pos[i] = {0};
for (int i = 1; i <= n; ++i) pos[a[i]].push_back(i);
{ // init save array
IT::build(1, 1, n);
for (int i = 1; i <= n; ++i)
IT::update(1, 1, n, i, n, 1);
saveL[0] = {0, 0};
for (int index = 1; index <= n; ++index) {
for (int i = 1; i < (int)pos[index].size(); ++i)
IT::update(1, 1, n, pos[index][i], n, -1);
for (int i = 1; i < (int)pos[index].size(); ++i) {
int p = pos[index][i];
saveL[p - 1] = IT::merge(saveL[0], IT::query(1, 1, n, 1, p - 1));
saveR[p] = IT::query(1, 1, n, p, n);
}
for (int i = 1; i < (int)pos[index].size(); ++i)
IT::update(1, 1, n, pos[index][i], n, -1);
}
}
auto chk = [&](int length) {
for (int index = 1; index <= n; ++index) {
for (int i = 1; i <= (int)pos[index].size() - length; ++i) {
int l = pos[index][i], r = pos[index][i + length - 1];
if (max(saveL[l - 1].mi, saveR[r].mi) -
min(saveL[l - 1].ma, saveR[r].ma) <= length) return true;
}
}
return false;
};
int le = 1, ri = n, answer = 1;
while (le <= ri) {
int mid = (le + ri) >> 1;
if (chk(mid)) le = (answer = mid) + 1;
else ri = mid - 1;
}
return answer;
}
#ifdef LOCAL
int main() {
int N;
assert(1 == scanf("%d", &N));
std::vector<int> A(N);
for (int i = 0; i < N; ++i) {
assert(1 == scanf("%d", &A[i]));
}
int result = sequence(N, A);
printf("%d\n", result);
return 0;
}
#endif
