import java.util.Scanner;

public class No45 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int[] v = new int[N];
        int[] dp = new int[N];

        for (int i = 0; i < N; i++) {
            v[i] = Integer.parseInt(sc.next());
        }

        if(N == 1){
            System.out.println(v[0]);
            return;
        }else if(N == 2){
            if(v[0] > v[1]){
                System.out.println(v[0]);
            }else{
                System.out.println(v[1]);
            }
        }else if(N == 3){
            if(v[0] + v[2] > v[1]){
                System.out.println(v[0] + v[2]);
            }else{
                System.out.println(v[1]);
            }
        }

        dp[0] = v[0];
        dp[1] = v[1];
        dp[2] = dp[0] + v[2];

        for (int i = 3; i < N; i++) {
            if(dp[i-3] > dp[i-2]){
                dp[i] = dp[i-3] + v[i];
            }else{
                dp[i] = dp[i-2] + v[i];
            }
        }

        System.out.println(dp[N-1]);
    }
}