import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int []V = new int[N];
		for(int i = 0; i < N; i++) {
			V[i] = scan.nextInt();
		}
		scan.close();
		if(N == 1) {
			System.out.println(V[0]);
			System.exit(0);
		}
		int []dp = new int[N];
		Arrays.fill(dp, 0);
		dp[0] = V[0];
		dp[1] = Math.max(V[0], V[1]);
		for(int i = 2; i < N; i++) {
			dp[i] = Math.max(dp[i - 1], dp[i - 2] + V[i]);
		}
		System.out.println(dp[N - 1]);

	}
}