Problem:
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Maximum Profit

You can obtain profits from foreign exchange margin transactions. For example, if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.

Write a program which reads values of a currency $R_t$ at a certain time $t$ ($t = 0, 1, 2, ... n-1$), and reports the maximum value of $R_j - R_i$ where $j > i$ .

Input

The first line contains an integer $n$. In the following $n$ lines, $R_t$ ($t = 0, 1, 2, ... n-1$) are given in order.

Output

Print the maximum value in a line.

Constraints

$2 \leq n \leq 200,000$

$1 \leq R_t \leq 10^9$

Sample Input 1

6
5
3
1
3
4
3

Sample Output 1

3

Sample Input 2

3
4
3
2

Sample Output 2

-1

Solution in C# (judge verdict: Wrong Answer)

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

namespace procon
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var list = new Dictionary<int, int>();

            for (int i = 0; i < n; i++)
            {
                list.Add(i, int.Parse(Console.ReadLine()));
            }

            // MIN?????????????????´???MAX?????????
            var min1 = list.FindMin(c => c.Value);
            var v1 = list.Where((e, index) => min1.Key < index);
            var dif1 = -1;
            if (v1.Count() > 0)
            {
                var max1 = v1.FindMax(c => c.Value);
                dif1 = max1.Value - min1.Value;
                dif1 = dif1 == 0 ? -1 : dif1;
            }

            // MAX?????????????????´???MIN?????????
            var min2 = list.FindMax(c => c.Value);
            var dif2 = -1;
            var v2 = list.Where((e, index) => index < min2.Key);
            if (v2.Count() > 0)
            {
                var max2 = v2.FindMin(c => c.Value);
                dif2 = max2.Value - min2.Value;
                dif2 = dif2 == 0 ? -1 : dif2;
            }

            Console.WriteLine(dif1 > dif2 ? dif1 : dif2 > 0 ? dif2 : -1);
        }
    }

    public static class IEnumerableExtensions
    {
        /// <summary>
        /// ????°?????????????????´????????????????
        /// </summary>
        public static TSource FindMin<TSource, TResult>(
            this IEnumerable<TSource> self,
            Func<TSource, TResult> selector)
        {
            return self.First(c => selector(c).Equals(self.Min(selector)));
        }

        /// <summary>
        /// ?????§????????????????´????????????????
        /// </summary>
        public static TSource FindMax<TSource, TResult>(
            this IEnumerable<TSource> self,
            Func<TSource, TResult> selector)
        {
            return self.First(c => selector(c).Equals(self.Max(selector)));
        }
    }
}