#include <fstream>

using namespace std;

ifstream cin ("oo.in");
ofstream cout ("oo.out");

int val[100100];
int dp[100100];

int main() {

    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    int n;
    cin>>n;

    for (int i=1; i<=n; i++){
        cin>>val[i];
    }

    for (int i=1; i<n; i++){
        dp[i] = max (dp[i-1] , dp[i-3] + val[i-3] + val[i-2]);
    }

    cout<<dp[n-1];

    return 0;
}