#include <iostream>
#include <vector>
using namespace std;

int main(){
    int N;
    cin >> N;
    vector<int> V(N, 0);
    for(int i=0;i<N;i++) cin >> V[i];

    vector<int> dp_o(N, -1000);
    vector<int> dp_x(N, -1000);

    dp_o[0] = V[0];
    dp_x[0] = 0;

    for(int i=1;i<N;i++){
        dp_o[i] = dp_x[i - 1] + V[i];
        dp_x[i] = max(dp_o[i - 1], dp_x[i - 1]);
    }

    int answer = max(dp_o[N - 1], dp_x[N - 1]);
    cout << answer << endl;
}