import java.util.Scanner;

public class 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 + 1];

		dp[0] = v[0];
		if (n > 1) dp[1] = Math.max(v[0], v[1]);
		for (int i = 2; i < n; i++) {
			dp[i] = Math.max(dp[i - 2] + v[i], dp[i - 1]);
		}
		System.out.println(dp[n - 1]);
	}
}