#include "bits/stdc++.h"
using namespace std;
const int MAX = 700000;
const int MOD = 1000000007;

long long  fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
	fac[0] = fac[1] = 1;
	finv[0] = finv[1] = 1;
	inv[1] = 1;
	for (int 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;
	}
}

// 二項係数計算
long long COM(int n, int k) {
	if (n < k) return 0;
	if (n < 0 || k < 0) return 0;
	return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
/*第二引数で第一引数を割ったときの切り上げの計算*/
long long int maxtime(long long int x, long long int y) {
	return(x + y - 1) / y;

}
/*最大公約数*/
long long int lcm(long long int number1, long long int number2) {
	long long int m = number1;
	long long int n = number2;

	if (number2 > number1) {
		m = number2;
		n = number1;
	}
	long long int s = -1;
	while (s != 0) {
		s = m % n;
		m = n;
		n = s;
	}
	return m;
}
/*最大公倍数*/
long long int gcd(long long int number1, long long int number2) {
	long long int m = number1;
	long long int n = number2;
	return m / lcm(m, n) * n;
}
/*逆元計算*/
long long int  modinv(long long a, long long m) {
	long long int b = m, u = 1, v = 0;
	while (b) {
		long long int t = a / b;
		a -= t * b; swap(a, b);
		u -= t * v; swap(u, v);
	}
	u %= m;
	if (u < 0) u += m;
	return u;
}
// index が条件を満たすかどうか
vector<long long int >meguru;
bool isOK(int index, int key) {
	if (meguru[index] >= key) return true;
	else return false;
}
// 汎用的な二分探索のテンプレ
int binary_search(int key) {
	int left = -1; //「index = 0」が条件を満たすこともあるので、初期値は -1
	int right = (int)meguru.size(); // 「index = a.size()-1」が条件を満たさないこともあるので、初期値は a.size()
	/* どんな二分探索でもここの書き方を変えずにできる！ */
	while (right - left > 1) {
		int mid = left + (right - left) / 2;

		if (isOK(mid, key)) right = mid;
		else left = mid;
	}
	/* left は条件を満たさない最大の値、right は条件を満たす最小の値になっている */
	return right;
}
long long modpow(long long a, long long n, long long mod) {
	long long res = 1;
	while (n > 0) {
		if (n & 1) res = res * a % mod;
		a = a * a % mod;
		n >>= 1;
	}
	return res;
}

int main() {
	int n;
	cin >> n;
	vector<long long int> v;
	for (int i = 0; i < n; i++) {
		long long int a;
		cin >> a;
		v.push_back(a);
	}
	int max = 0;
	long long int ans = 0;
	for (int i = 0; i < v.size(); i++) {
		if (v[i] < max) {
			ans = ans + max - v[i];
		}
		else if (v[i] > max) {
			max = v[i];
		}
	}
	cout << ans;
}
#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;

#define FOR(i,a,b) for (int i = a; i < b; ++i)
#define FORR(i,a,b) for (int i = b - 1; i >= a; --i)
#define REP(i,n) FOR(i,0,n)
#define REPR(i,n) FORR(i,0,n)

int main() {
	ll N;
	cin >> N;
	ll A, high = 0, ans = 0;

	REP (i, N) {
		cin >> A;
		high = max(A, high);
		ans += high - A;
	}

	cout << ans << endl;
	return 0;
}