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.IO;
using System.Reflection;
using System.Collections.Generic;
using System.Text;

namespace AOJ
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            var dic = new Dictionary<int, int>();
            int? maxProf = null;
            for (int i= 0; i < n; ++i)
            {
                dic.Add(i,int.Parse(Console.ReadLine()));
            }
            for(int i = 0; i < n; ++i)
            {
                for(int j = i+1; j < n-1; ++j)
                {
                    if(maxProf == null)
                    {
                        maxProf = dic[j] - dic[i];
                    }
                    else
                    {
                        if(maxProf < dic[j] - dic[i])
                        {
                            maxProf = dic[j] - dic[i];
                        }
                    }
                }
            }
            Console.WriteLine(maxProf);
        }
 
    }
}