using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

static class ConveyorBeltSushi
{
    static void Main()
    {
    	// 何にも使わない
	    int count = int.Parse(Console.ReadLine());
	    
	    var deliciousness = Console.ReadLine().Split(' ').Select(int.Parse);
	    
	    var sumDeliciousness = deliciousness.Chunk(4).Select(x => {
	    	switch(x.Count()) 
	    	{
	    		case 1:
	    		return x.Max();
	    		case 2:
	    		return x.Max();
	    		case 3:
	    		return Math.Max(x[0] + x[2], x[1]);
	    		case 4:
	    		return Math.Max(x[0] + x[2], x[1] + x[3]);
	    		default:
	    		return 0;
	    	}}).Sum();
	    	
	    	Console.WriteLine(sumDeliciousness);
   }
}