#pragma region Headers
#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <codecvt>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif
#pragma endregion

using namespace std;
#pragma region Macros
#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0, a1, a2, a3, a4, x, ...) x
#define debug_1(x1) cout << #x1 << ": " << x1 << endl
#define debug_2(x1, x2) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << endl
#define debug_3(x1, x2, x3) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " << x3 << endl
#define debug_4(x1, x2, x3, x4) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " << x3 << ", " #x4 << ": " << x4 << endl
#define debug_5(x1, x2, x3, x4, x5) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " << x3 << ", " #x4 << ": " << x4 << ", " #x5 << ": " << x5 << endl
#ifdef _DEBUG
#define debug(...)                                                        \
    CHOOSE((__VA_ARGS__, debug_5, debug_4, debug_3, debug_2, debug_1, ~)) \
    (__VA_ARGS__)
#else
#define debug(...)
#endif
#pragma region end

#pragma region Libraries
template <typename T>
string to_string(T o)
{
    stringstream s;
    s << o;
    return s.str();
}

template <typename T>
string to_string(vector<T> v)
{
    stringstream s;
    s << "[";
    for (auto i = 0; i < v.size(); i++)
    {
        s << to_string(v.at(i));
        if (i != v.size() - 1)
        {
            s << ", ";
        }
    }
    s << "]";
    return s.str();
}

template <typename T>
ostream &operator<<(ostream &o, const vector<T> &obj)
{
    o << to_string(obj);
    return o;
}

template <typename T>
string to_string(vector<vector<T>> m)
{
    stringstream s;
    s << "[" << endl;
    for (auto i = 0; i < m.size(); i++)
    {
        auto v = m[i];
        s << "  "
          << "#" << i << ":"
          << " " << to_string(v);
        s << ", " << endl;
    }
    s << "]";
    return s.str();
}

template <typename T>
ostream &operator<<(ostream &o, const vector<vector<T>> &obj)
{
    o << to_string(obj);
    return o;
}

template <typename K, typename V>
string to_string(pair<K, V> p)
{
    stringstream s;
    s << "pair(" << to_string(p.first) << ", " << to_string(p.second) << ")";
    return s.str();
}

template <typename K, typename V>
ostream &operator<<(ostream &o, const pair<K, V> &obj)
{
    o << to_string(obj);
    return o;
}

template <typename K, typename V>
string to_string(map<K, V> m)
{
    stringstream s;
    s << "{" << endl;
    for (const auto &p : m)
    {
        s << "  " << to_string(p.first) << ": " << to_string(p.second) << "," << endl;
    }
    s << "}";
    return s.str();
}

template <typename K, typename V>
ostream &operator<<(ostream &o, const map<K, V> &obj)
{
    o << to_string(obj);
    return o;
}

template <typename T>
string to_string(set<T> ss)
{
    stringstream s;
    s << "set"
      << "{";
    for (auto itr = ss.begin(); itr != ss.end(); itr++)
    {
        s << to_string(*itr);
        if (next(itr, 1) != ss.end())
        {
            s << ", ";
        }
    }
    s << "}";
    return s.str();
}

template <typename T>
ostream &operator<<(ostream &o, const set<T> &obj)
{
    o << to_string(obj);
    return o;
}

template <typename T>
string to_string(queue<T> q)
{
    auto temp = queue<T>{};
    stringstream s;
    s << "queue{";
    while (!q.empty())
    {
        auto top = q.front();
        s << to_string(top) << ", ";
        q.pop();
        temp.push(top);
    }
    s << "}";

    while (!temp.empty())
    {
        auto top = temp.front();
        temp.pop();
        q.push(top);
    }

    return s.str();
}

template <typename T>
ostream &operator<<(ostream &o, const queue<T> &obj)
{
    o << to_string(obj);
    return o;
}
#pragma endregion

typedef long long ll;

int main()
{
    cin.tie(0);
    ll n;
    cin >> n;

    ll sum = 0;
    ll cur_max = 0;
    for (auto i = 0; i < n; i++)
    {
        ll a;
        cin >> a;
        if (a > cur_max)
        {
            cur_max = a;
        }
        else
        {
            sum += cur_max - a;
        }
    }
    cout << sum << endl;

    return 0;
}


Measured memory_bytes: 3196