import java.util.*;
import java.awt.geom.*;
import java.io.*;
public class Main {
	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+2];
		for(int i = 0; i < N; i++) {
			dp[i+1] = Math.max(dp[i], dp[i+1]);
			dp[i+2] = Math.max(dp[i] + V[i], dp[i+2]);
		}
		dp[N+1] = Math.max(dp[N+1], dp[N]);
		System.out.println((dp[N+1]));
 	}
}