#include <bits/stdc++.h>
#pragma GCC optimize("O2")
using namespace std;
const int INF = 0x3f3f3f3f, N = 1e6 + 5, MOD = 1e9 + 7;
const long long INF_LL = 0x3f3f3f3f3f3f3f3fLL;
template <typename T>
inline int getplc(T x, int y) {
  return (x >> y) & 1;
}
template <typename T>
T square(T x) {
  return x * x;
}
long long qpow(long long a, long long b = MOD - 2, long long _MOD = MOD) {
  long long res = 1;
  for (; b; b >>= 1, a = a * a % _MOD) {
    if (b & 1) res = res * a % _MOD;
  }
  return res;
}
template <typename T>
T Smax(T x) {
  return x;
}
template <typename T, typename... Args>
T Smax(T a, Args... args) {
  return max(a, Smax(args...));
}
template <typename T>
T Smin(T x) {
  return x;
}
template <typename T, typename... Args>
T Smin(T a, Args... args) {
  return min(a, Smin(args...));
}
template <typename T>
void errl(istream_iterator<string> it) {}
template <typename T, typename... Args>
void errl(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << endl;
  errl(++it, args...);
}
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << "=" << a << " # ";
  err(++it, args...);
}
int a[N];
void Solve() {
  int n, mx = INT_MIN, ans = 0;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    mx = max(a[i], mx);
    ans += mx - a[i];
  }
  cout << ans << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  Solve();
  return 0;
}
