import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Back_2579 {
    public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(br.readLine());

        int[] DP = new int[N + 1];
        int[] arr = new int[N + 1];

        for (int i = 1; i <= N; i++) {
            arr[i] = Integer.parseInt(br.readLine());
        }

        DP[1] = arr[1];

        if (N >= 2) {
            DP[2] = arr[1] + arr[2];
        }

        for (int i = 3; i <= N; i++) {
            DP[i] = Math.max(DP[i - 2], DP[i - 3] + arr[i - 1]) + arr[i];
        }
        System.out.println(DP[N]);
    }
}