/* package whatever; // don't place package name! */

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

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		
		int a[]=new int[n+1];
		for(int i=1;i<=n;i++)
		a[i]=sc.nextInt();
		
		int dp[]=new int[n+1];
		
		dp[1]=a[1];
		dp[2]=Math.max(dp[1],a[2]);
		
		for(int i=3;i<=n;i++)
		dp[i]=Math.max(dp[i-1],a[i]+dp[i-2]);
		
		System.out.println(dp[n]);
		
	}
}