using System;

namespace HeroGame
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string[] input = Console.ReadLine().Split(' ');
            int[] safehouses = new int[input.Length];
            for (int i = 0; i < input.Length; i++)
            {
                safehouses[i] = int.Parse(input[i]);
            }

            int greatestDistance = 0;
            for (int i = 0; i < n; i++)
            {
                int minDistance = int.MaxValue;
                for (int j = 0; j < safehouses.Length; j++)
                {
                    int distance = Math.Abs(i - safehouses[j]);
                    if (distance < minDistance)
                    {
                        minDistance = distance;
                    }
                }

                if (minDistance > greatestDistance)
                {
                    greatestDistance = minDistance;
                }
            }

            Console.WriteLine(greatestDistance);
        }
    }
}