#include <bits/stdc++.h>
using namespace std;
struct IoSetup {
  IoSetup() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} IoSetup;
using Int = __int128_t;
using ll = long long;
using pii = pair<int, int>;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr int SMOD = 1000000007;
constexpr int NMOD = 998244353;
constexpr int dx[] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr int dy[] = {0, -1, 0, 1, -1, 1, -1, 1};
inline bool inside(int x, int y, int w, int h) {
  return (x >= 0 && y >= 0 && x < w && y < h);
}
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) return (a = b, 1);
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) return (a = b, 1);
  return 0;
}
signed main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (auto &&i : a) cin >> i;
  int sum = 0;
  int mv = a[0];
  for (auto &&i : a) {
    sum += max(0, mv - i);
    chmax(mv, i);
  }
  cout << sum << endl;
  return 0;
}
