#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  int x = 0, rta = 0;
  for (int i = 0; i < n; i++) {
    x = max(arr[i], x);
    rta += (x - arr[i]);
  }
  cout << rta << endl;
}
