#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; ++i) cin >> v[i];
  int count = 0;
  int mx = 0;
  for (int i = 0; i < n; ++i) {
    mx = max(mx, v[i]);
    count += mx - v[i];
  }
  cout << count << "\n";
  return 0;
}
