import java.util.*;

public class Main {
    
    static int N;
    static int[] V = new int[1000];
    static int[] memo = new int[1000];
    
    public static int  rec(int i){
        int ret;
        if(i >= N){ret = 0;}
        else{
            if(memo[i+1] == -1){ memo[i+1] = rec(i+1); }
            if(memo[i+2] == -1){ memo[i+2] = rec(i+2); }
            ret = Math.max(memo[i+1], memo[i+2]+V[i]);
            //System.out.println(i+":"+memo[i+1]+ " " +(memo[i+2]+V[i]));
        }
        
        return ret;
    }
    
    public static void main(String[] args) throws Exception {
        // Here your code !
        Scanner sc = new Scanner(System.in);
        N = sc.nextInt();
        
        for(int i=0; i<N; i++) V[i] = sc.nextInt();
        Arrays.fill(memo,-1);
        System.out.println(rec(0));
        
        
    }
}