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;

namespace Test
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var nums = new int[N];
            for (int i = 0; i < nums.Length; i++)
            {
                nums[i] = int.Parse(Console.ReadLine());
            }

            var min = nums[0];
            int? oldProfit = null;
            int? nowProfit = null;
            int? max = null;
            for (int i = 1; i < nums.Length; i++)
            {
                if (min < nums[i])
                {
                    if (max == null)
                    {
                        nowProfit = nums[i] - min;
                        max = nums[i];
                    }
                    else if (max < nums[i])
                    {
                        nowProfit = nums[i] - min;
                        max = nums[i];
                    }
                }
                else if (min > nums[i])
                {
                    if (oldProfit < nowProfit) oldProfit = nowProfit;
                    if (nowProfit.HasValue == false)
                    {
                        oldProfit = nums[i] - min;
                    }
                    else
                    {
                        oldProfit = nowProfit;
                    }
                    min = nums[i];
                    nowProfit = null;
                }
            }

            if (oldProfit < nowProfit) Console.WriteLine(nowProfit);
            else if (nowProfit.HasValue == true) Console.WriteLine(nowProfit);
            else if (oldProfit.HasValue == true) Console.WriteLine(oldProfit);
           
        }
    }
}