#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 mx = 0, sum = 0;
  for (int i = 0; i < (n); i++) {
    mx = max(v[i], mx);
    sum += mx - v[i];
  }
  cout << sum << endl;
}
