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

public class Amatsuki
{
    private static List<int> sushiList;

    public static void Main()
    {
        Console.ReadLine();
        sushiList = Console.ReadLine().Split(new char[] {' '}).Select(x => int.Parse(x)).ToList();
        sushiList.Add(0);
        var eatenSushi = 0;

        do
        {
            eatenSushi += ChoiseSushi();
        } while (sushiList.Sum() != 0);

        Console.WriteLine(eatenSushi);
        Console.ReadKey();
    }

    private static int ChoiseSushi()
    {
        var deliciousSushiIndex = sushiList
            .Select((x, i) => new { Index = i, Sushi = x })
            .OrderByDescending(x => x.Sushi)
            .First()
            .Index;

        if (CompareSushi(deliciousSushiIndex))
        {
            return EatSushi(deliciousSushiIndex - 1) + EatSushi(deliciousSushiIndex + 1);
        }
        else
        {
            return EatSushi(deliciousSushiIndex);
        }
    }

    private static int EatSushi(int index)
    {
        var tmp = sushiList[index];
        sushiList[index] = 0;

        if (index + 1 < sushiList.Count)
        {
            sushiList[index + 1] = 0;
        }

        if (index != 0)
        {
            sushiList[index - 1] = 0;
        }

        return tmp;
    }

    private static bool CompareSushi(int index)
    {
        var comp = 0;

        if (index + 1 < sushiList.Count)
        {
            comp += sushiList[index + 1];
        }

        if (index != 0)
        {
            comp += sushiList[index - 1];
        }

        return (comp > sushiList[index]) ;
    }
}