#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N; cin >> N;
    vector<int> A(N);
    rep(i,N) cin >> A[i];

    vector<pair<int,int>> v = {{A[0], 1}};
    for(int i = 1; i < N; i++) {
        if(v.back().first == A[i]) v.back().second++;
        else v.push_back({A[i], 1});
    }

    A.clear();
    for(auto [x, c] : v) A.push_back(c);
    N = int(A.size());
    int dp[N + 1][2] = {};
    for(int i = 0; i < N; i++) {
        dp[i + 1][1] = max(dp[i + 1][1], dp[i][0] + A[i]);
        dp[i + 1][0] = max(dp[i + 1][0], max(dp[i][0], dp[i][1]));
    }
    cout << max(dp[N][0], dp[N][1]) << "\n";
}