import java.util.Scanner;


public class Main_yukicoder45 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] v = new int[n];
        for (int i = 0; i < n; i++) {
        	v[i] = sc.nextInt();
        }

        int[] dp = new int[n];
        int max = 0;
        for (int i = 0; i < n; i++) {
        	dp[i] = v[i];
        	
        	for (int j = Math.max(0, i - 3); j < i - 1; j++) {
        		dp[i] = Math.max(dp[i], dp[j] + v[i]);
        	}
        	max = Math.max(max, dp[i]);
        }

        System.out.println(max);
        
        sc.close();
    }
}