import java.util.Scanner;

public class Main {
	static boolean memo[];
	static int ans, min;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		if (n > 1) {
			int[] dp = new int[n];
			int[] v = new int[n];
			for (int i = 0; i < n; i++) {
				v[i] = sc.nextInt();
			}
			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]);
			}
			int max = 0;
			for (int i = 0; i < n; i++) {
				max = Math.max(max, dp[i]);
			}
			System.out.println(max);
		} else {
			int v = sc.nextInt();
			System.out.println(v);
		}

	}
}