using System;

using System.Linq;

using System.IO;

using System.Text;

using System.Collections;

using System.Collections.Generic;

using c = System.Console;

​

class Solution {

    static void Main(string[] args)

    {

        var e = int.Parse(c.ReadLine())>0

        ? c.ReadLine().Split(' ').Select(x=>int.Parse(x)).OrderBy(x => Math.Abs(x)).ToList()

        : null;

        c.WriteLine(e==null?0:e[1]>0&&e.Any(x=>x==-e[0])?e[1]:e[0]);

    }

}

​