// 这是我的代码
#include <iostream>
(30316)#include <vector>
using namespace std;
int main() {
int n;
cin >> n;
if (n < 3) {
cout << n;
return 0;
}
vector<int> a(n);
for(int i = 0; i < n; ++i) {
cin >> a[i];
}
int res = 2;
vector<int> dp(n);
// vector<int> idx(n); 应该把长度相同的前一个下标记录在数组里
unordered_map<int, vector<int>> m;
dp[0] = 1, dp[1] = 2;
m[0] = {-1}, m[1] = {0};
for (int i = 2; i < n; ++i) {
for (int j = 0; j < i; ++j) {
for (int k = 0; k < m[j].size(); ++k) {
if (m[j][k] == -1 || a[m[j][k]] == a[i]) {
if (dp[j] + 1 >= dp[i]) {
dp[i] = dp[j] + 1;
m[i].push_back(j);
}
}
}
}
res = max(res, dp[i]);
}
cout << res;
return 0;
}
