Problem:
Score : 300 points

Problem Statement

N persons are standing in a row. The height of the i-th person from the front is A_i.

We want to have each person stand on a stool of some heights - at least zero - so that the following condition is satisfied for every person:

Condition: Nobody in front of the person is taller than the person. Here, the height of a person includes the stool.

Find the minimum total height of the stools needed to meet this goal.

Constraints

1 \leq N \leq 2\times 10^5

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 \ldots A_N

Output

Print the minimum total height of the stools needed to meet the goal.

Sample Input 1

5
2 1 5 4 3

Sample Output 1

4

If the persons stand on stools of heights 0, 1, 0, 1, and 2, respectively, their heights will be 2, 2, 5, 5, and 5, satisfying the condition.

We cannot meet the goal with a smaller total height of the stools.

Sample Input 2

5
3 3 3 3 3

Sample Output 2

0

Giving a stool of height 0 to everyone will work.

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

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

namespace ABC176
{
    using static Ex;
    public class Solve
    {
        public static void Main(string[] args)
        {
            new ABC_C();
        }
    }
    public class ABC_A
    {
        public ABC_A()
        {
            var (n, x, t) = ReadIntArray().ToTpl3();
            int ans = n / x;
            if (n % x > 0) ans++;
            ans *= t;
            ans.Cw();
        }
    }
    public class ABC_B
    {
        public ABC_B()
        {
            var n = Read;
            int ans = 0;
            foreach (var v in n)
            {
                var i = v - '0';
                ans += i;
                ans %= 9;
            }
            (ans % 9 == 0).YesNo();
        }
    }
    public class ABC_C
    {
        public ABC_C()
        {
            var n = ReadLong;
            var a = ReadLongArray();
            long ans = 0;
            long max = 0;
            foreach (var i in a)
            {
                ans += Math.Max(0, max - i);
                Maxs(ref max, i);
            }
            ans.Cw();
        }
    }

    public static class Ex
    {
        public static void Cw(this object s) { Console.WriteLine(s); }



        public static bool Mins<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) > 0) { a = b; return true; } return false; }
        public static bool Maxs<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
        public static void Swap<T>(ref T a, ref T b) { var t = b; b = a; a = t; }
        public static void Swap<T>(List<T> list, int i, int j) { T tmp = list[j]; list[j] = list[i]; list[i] = tmp; }

        public static long Lcm(int x, int y) { return x / Gcd(x, y) * y; }
        public static long Gcd(long m, long n) { if (n == 0) return m; return Gcd(n, m % n); }
        public static List<string> FastSort(this List<string> s) { s.Sort(StringComparer.Ordinal); return s.ToList(); }
        public static void yesno(this bool b) { (b ? "yes" : "no").Cw(); }
        public static void YesNo(this bool b) { (b ? "Yes" : "No").Cw(); }
        public static void YESNO(this bool b) { (b ? "YES" : "NO").Cw(); }

        public static string Read { get { return Console.ReadLine().Trim(); } }
        public static int ReadInt { get { return int.Parse(Read); } }
        public static long ReadLong { get { return long.Parse(Read); } }
        public static double ReadDouble { get { return double.Parse(Read); } }
        public static string[] ReadArray() { return Read.Split(' '); }
        public static int[] ReadIntArray() { return Read.Split(' ').Select(int.Parse).ToArray(); }
        public static long[] ReadLongArray() { return Read.Split(' ').Select(long.Parse).ToArray(); }
        public static string[] ReadArray(long N) { var v = new string[N]; for (long i = 0; i < N; ++i) v[i] = Read; return v; }
        public static int[] ReadIntArray(long N) { var v = new int[N]; for (long i = 0; i < N; ++i) v[i] = ReadInt; return v; }
        public static long[] ReadLongArray(long N) { var v = new long[N]; for (long i = 0; i < N; ++i) v[i] = ReadLong; return v; }

        public static (T, T) ToTpl2<T>(this T[] v) { return (v[0], v[1]); }
        public static (T, T, T) ToTpl3<T>(this T[] v) { return (v[0], v[1], v[2]); }
        public static (T, T, T, T) ToTpl4<T>(this T[] v) { return (v[0], v[1], v[2], v[3]); }
        public static (T, T, T, T, T) ToTpl5<T>(this T[] v) { return (v[0], v[1], v[2], v[3], v[4]); }
    }
}