import java.util.*;

public class _2579{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] stair = new int[N+1];
        for(int i=1; i<=N; i++){
            stair[i] = sc.nextInt();
        }

        int[] dp = new int[N+1];
        
        switch (N) {
            case 1:
                System.out.println(stair[1]);
                break;

            case 2:
                System.out.println(stair[1]+stair[2]);
                break;

            case 3:
                System.out.println(Math.max(stair[1] + stair[3], stair[2] + stair[3]));
                break;
        
            default:
                dp[1] = stair[1];
                dp[2] = stair[1] + stair[2];
                dp[3] = Math.max(stair[1] + stair[3], stair[2] + stair[3]);
                for(int i=4; i<=N; i++){
                    dp[i] = Math.max(dp[i-2] + stair[i], dp[i-3] + stair[i-1] + stair[i]);
                }
                System.out.println(dp[N]);
                break;
        }

        sc.close();
    }
}