import java.io.*;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;
 
public class Main {
    public static void main (String[] args) throws IOException
    {
    	Scanner sc = new Scanner(System.in);
    	int N = sc.nextInt();
    	int V[]= new int [N+1];
    	int f[] = new int [N+1];
    	
    	
    	for (int i = 1 ; i <= N ; i++){
    		V[i] = sc.nextInt();
    	}
    	
    	if (N == 1){ 
    		System.out.println(V[1]);
    	}
    	else if (N==2){
    		System.out.println(Math.max(V[1],V[2]));
    	}
    	
    	else {

    	f[1] = V[1];
    	f[2] = Math.max(V[1],V[2]);
    	
    	for (int i = 3 ; i <= N ; i++){
    		f[i] = Math.max(f[i-2] + V[i],f[i-1]);
    	}
    	
    	System.out.println(f[N]);
    	}
    }	
}