#include<bits/stdc++.h>
using namespace std;

int main(){
    long N; cin >> N;
    long cnt = 0;
    long last = -1;
    vector<long> Acnt(2, 0);
    while(N--){
        long a; cin >> a;
        if(a == last) cnt++;
        else{
            Acnt.push_back(cnt);
            cnt = 1;
            last = a;
        }
    }
    Acnt.push_back(cnt);
    
    vector<long> dp(Acnt.size(), 0);
    for(long i = 3; i < Acnt.size(); i++){
        dp[i] = max(dp[i], dp[i - 1]);
        dp[i] = max(dp[i], dp[i - 2] + Acnt[i]);
        dp[i] = max(dp[i], dp[i - 3] + Acnt[i]);
    }
    cout << dp[Acnt.size() - 1] << '\n';
}