#include <bits/stdc++.h>
using namespace std;

#pragma region macros_and_aliases

#define rep(i, n) for(long long i = 0; i < (n); i++)
#define rrep(i, n) for(long long i = (n)-1; i > -1; i--)
#define Rep(i, m, n) for(long long i = (m); i < (n); i++)
#define rRep(i, m, n) for(long long i = (n)-1; i >= (m); i--)
#define REP(i, m, n, p) for(long long i = m; i < n; i += p)
#define foa(s, v) for(auto &s : v)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define pq priority_queue
#define bcnt(n) __builtin_popcountll(n)
#define endk endl
#define ednl endl
#define enld endl

using ll = long long;
using ld = long double;
using vb = vector<bool>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using mll = map<long long, long long>;
using pll = pair<long long, long long>;
using qll = queue<long long>;
using sll = set<long long>;
using vpll = vector<pair<long long, long long>>;
template <class T = ll>
using V = vector<T>;
template <class T = ll>
using VV = V<V<T>>;
template <class T = ll>
using VVV = V<V<V<T>>>;
//昇順pq(小さい方から取り出す)
template <class T = ll>
using pqup = priority_queue<T, vector<T>, greater<T>>;
//降順pq(大きい方から取り出す)
template <class T = ll>
using pqdn = priority_queue<T>;

#define debug(var)              \
	std::cout << #var << " : "; \
	view(var)
template <typename T>
void view(T e) {
	std::cout << e << std::endl;
}
template <typename T>
void view(const std::vector<T> &v) {
	for(const auto &e : v) {
		std::cout << e << " ";
	}
	std::cout << std::endl;
}
template <typename T>
void view(const std::vector<std::vector<T>> &vv) {
	cout << "\n";
	for(const auto &v : vv) {
		view(v);
	}
}

template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
	os << p.first << " " << p.second;
	return os;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
	is >> p.first >> p.second;
	return is;
}
#pragma endregion

#pragma region constants

long long const limLL = 9223372036854775807;  // POW(2,63)-1 ~ 9.22e18
long long const dekai = 3e16;
const long double pi = acos(-1);
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int ddx[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddy[8] = {-1, 0, 1, -1, 1, -1, 0, 1};

const int mod = 1000000007;
// const int mod = 998244353;
#pragma endregion

#pragma region basic_procedure

template <class T>
inline bool isin(T x, T lef, T rig) {
	return ((lef <= x) && (x < rig));
}
template <class T>
inline bool isin(T x, T y, T lef, T rig) {
	return isin(x, lef, rig) && isin(y, lef, rig);
}
template <class T>
inline bool isin(T X, T lefX, T rigX, T Y, T lefY, T rigY) {
	return isin(X, lefX, rigX) && isin(Y, lefY, rigY);
}

template <class T>
inline bool chmin(T &a, T b) {
	if(a > b) {
		a = b;
		return true;
	}
	return false;
}
template <class T>
inline bool chmax(T &a, T b) {
	if(a < b) {
		a = b;
		return true;
	}
	return false;
}

void Yes(bool f = 1) { cout << (f ? "Yes" : "No") << "\n"; }
void No() { cout << "No\n"; }
void YES(bool f = 1) { cout << (f ? "YES" : "NO") << "\n"; }
void NO() { cout << "NO\n"; }
void err() { cout << -1 << "\n"; }

vector<long long> vin(long long n) {  //整数n個の入力を受け取ってベクトルに突っ込んで返す
	vector<long long> v(n);
	for(long long i = 0; i < n; i++) {
		cin >> v[i];
	}
	return v;
}

//ベクトルの出力(検証済)
// vectorの中身を出力する 答えの出力に利用可能
template <class T>
void vout(vector<T> &v, bool tate = 0) {
	if(v.size() > 0) {
		for(auto it = v.begin(); it < v.end(); it++) {
			cout << *it;
			if(it != v.end() - 1) {
				if(tate)
					cout << endl;
				else
					cout << " ";
			}
		}
	}
	cout << endl;
}

template <class T>
void add(vector<T> &v, T val) {	 //ベクトルの各要素に加算
	for(auto &a : v) a += val;
	return;
}

// vectorの中身を数える map<要素,個数>を返す
template <class T>
map<T, long long> cntv(vector<T> v) {
	map<T, long long> m;
	for(auto &g : v) {
		if(m.count(g))
			m[g]++;
		else
			m[g] = 1;
	}
	return m;
}

//配列圧縮(検証済)
//{1,36,1,3,8,-2,-92}を
//{2, 5,2,3,4, 1,  0}にする
template <class T>
vector<long long> press(vector<T> &v) {
	long long n = v.size();
	vector<long long> w(n);
	map<T, long long> m;
	for(T &p : v) m[p] = 0;
	long long i = 0;
	for(auto &p : m) {
		p.second = i;
		i++;
	}
	for(long long i = 0; i < n; i++) w.at(i) = m[v.at(i)];
	return w;
}

template <class T>
T divup(T a, T b) {
	//端数繰りあがり割り算
	assert(b != 0);
	T x = abs(a);
	T y = abs(b);
	T z = (x + y - 1) / y;
	if((a < 0 && b > 0) || (a > 0 && b < 0))
		return -z;
	else if(a == 0)
		return 0;
	else
		return z;
}

long long POW(long long a, long long n) {
	// 整数のとき限定の普通のPOW関数
	//標準機能のpow(a,n)は整数だとバグるのでこちらを使う
	long long res = 1;
	while(n > 0) {
		if(n & 1) res = res * a;
		a = a * a;
		n >>= 1;
	}
	return res;
}

template <class T>
int sgn(T x) {	//符号関数
	if(x < 0) return -1;
	if(x == 0) return x;
	return 1;
}

long long modpow(long long a, long long n, long long mod) {	 // a^n mod
	long long res = 1;
	while(n > 0) {
		if(n & 1) res = res * a % mod;
		a = a * a % mod;
		n >>= 1;
	}
	return res;
}

long long modinv(long long a, long long mod) {	// a^{-1} mod
	// modとaが互いに素のときのみ有効(数学的に逆元が一意に定まるのがそのときのみ)
	return modpow(a, mod - 2, mod);
}

vvll comb(100, vll(100, -1));
long long com(long long n, long long k) {  //普通の二項計数(overflowに注意)
	assert(n < 100 && k < 100);
	if(n < k || k < 0 || n < 0) return 0;
	if(comb[n][k] != -1) return comb[n][k];
	ll res;
	if(n - k < k)
		res = com(n, n - k);
	else if(k == 0)
		res = 1;
	else
		res = com(n - 1, k - 1) + com(n - 1, k);
	comb[n][k] = res;
	return res;
}

// nCk modを求める
const ll MAX = 5100000;
// この値は求める二項計数の値に応じて変える
// MAX=3*10^7のとき1900msほど、ほぼ比例
// MAX=5*10^6程度ならそれほど気にしなくてよい(300ms程)
long long fac[MAX], finv[MAX], inv[MAX];

void cominit() {
	// テーブルを作る前処理
	fac[0] = fac[1] = 1;
	finv[0] = finv[1] = 1;
	inv[1] = 1;
	for(ll i = 2; i < MAX; i++) {
		fac[i] = fac[i - 1] * i % mod;
		inv[i] = mod - inv[mod % i] * (mod / i) % mod;
		finv[i] = finv[i - 1] * inv[i] % mod;
	}
}
long long commod(ll n, ll k) {	// 二項係数計算
	if(n < k) return 0;
	if(n < 0 || k < 0) return 0;
	return fac[n] * (finv[k] * finv[n - k] % mod) % mod;
}
long long pmod(ll n, ll k) {  //順列計算
	if(n < k) return 0;
	if(n < 0 || k < 0) return 0;
	return fac[n] * finv[n - k] % mod;
}
long long hmod(ll n, ll k) {  // nHk計算
	// n個の区別しないoを区別するk個の箱に入れる方法の総数
	//(n+k-1)C(k-1)と等しい
	return commod(n + k - 1, n);
}
#pragma endregion

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	// cout << fixed << setprecision(15);
	ll n;
	cin >> n;
	vll a = vin(n);
	ll ans = 0;
	ll tp = a[0];
	rep(i, n - 1) {
		if(a[i + 1] <= a[i]) {
			ans += -a[i + 1] + a[i];
			a[i + 1] = a[i];
		} else {
		}
	}
	cout << ans << endl;
}

Measured memory_bytes: 4760