import java.util.*;
import java.lang.*;
import java.io.*;

class Ideone{
	public static void main(String[] args) throws Exception{
		// your code goes here
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int N = Integer.parseInt(br.readLine());
	    String[] prm = br.readLine().split(" ");
	    ArrayList<Integer> dish = new ArrayList<Integer>();
	    for(String st:prm){
	        dish.add(Integer.parseInt(st));
	    }
	    calc(0,0,dish);
	    System.out.println(max);
	    
	}
    private static int max = 0;
    private static HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();
    private static void calc(int ans,int idx,ArrayList<Integer> dish){
        if(map.containsKey(idx) && map.get(idx) > ans){
            return;
        }
        map.put(idx,ans);
        if(idx >= dish.size()){
            max = Math.max(ans,max);
            return;
        }
        calc(ans+dish.get(idx),idx+2,dish);
        calc(ans,idx+1,dish);
        return;
    }
}