using System;

using System.Collections.Generic;

​

namespace MinimumAmount

{

    class Program

    {

        static void Main(string[] args)

        {

            Console.Write("n = ");

            if (!int.TryParse(Console.ReadLine(), out int n) || n < 1 || n > 10000)

            {

                Console.WriteLine("Invalid n!");

                return;

            }

            var prices = new List<int>(n);

            for (int i = 0; i < prices.Capacity; i++)

            {

                if (!int.TryParse(Console.ReadLine(), out int price) ||

                    price < 1 || price > Math.Pow(10, 7))

                {

                    Console.WriteLine("Invalid price!");

                    return;

                }

                prices.Add(price);

            }

            Console.WriteLine(calculateAmount(prices));

        }

​

        public static long calculateAmount(List<int> prices)

        {

            long amount = 0;

            for (int i = 0; i < prices.Count; i++)

            {

                if (i == 0)

                {

                    amount += prices[i];

                }

                else

                {

                    int min = int.MaxValue;

                    for (int j = 0; j < i; j++)

                    {

                        min = Math.Min(min, prices[j]);

                    }

                    amount += Math.Max(prices[i] - min, 0);

                }

            }

            return amount;

        }

    }

}

​