#include <bits/stdc++.h>
using namespace std;
using ll = long long;
constexpr char NL = '\n';
constexpr int MOD = 1e9 + 7;
struct safe_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
void solve() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; ++i) {
    cin >> v[i];
  }
  int tallest = v[0], ans = 0;
  for (int i = 1; i < n; ++i) {
    if (v[i] > tallest) {
      tallest = v[i];
    } else {
      ans += tallest - v[i];
    }
  }
  cout << ans << NL;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  solve();
  return 0;
}
