#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    int N;
    cin >> N;
    int A[N];
    for (int i = 0; i < N; i++) {
        cin >> A[i];
    }
    vector<pair<int, int>> b;
    b.push_back(make_pair(A[0], 1));
    for (int i = 1; i < N; i++) {
        if (A[i] == (b.back()).first) {
            (b.back()).second++;
        } else {
            b.push_back(make_pair(A[i], 1));
        }
    }
    int l = b.size();
    int dp[l + 1]{};
    dp[1] = b[0].second;
    if (l == 1) {
        cout << dp[1] << "\n";
        return 0;
    }
    dp[2] = max(dp[1], b[1].second);
    for (int i = 2; i < l; i++) {
        dp[i + 1] = max(dp[i - 1], max(dp[i - 2], dp[i - 1]) + b[i].second);
    }
    cout << max(dp[l],dp[l - 1]) << "\n";
    // for (auto i : b) {
    //     cout << i.first << " " << i.second << "\n";
    // }
    return 0;
}