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

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		int eated = 0, not_eated = 0, prev_eated = 0, prev_not_eated = 0;
		
		for(int i = 0; i < N; i++){
			final int v = sc.nextInt();
			
			eated = prev_not_eated + v;
			not_eated = Math.max(prev_eated, prev_not_eated);
			
			prev_eated = eated;
			prev_not_eated = not_eated;
		}
		
		System.out.println(Math.max(prev_eated, prev_not_eated));
		
	}
	
}