#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 result = 0;
  int maxim = v[0];
  for (int i = 1; i < n; i++) {
    maxim = max(maxim, v[i]);
    result += maxim - v[i];
  }
  cout << result;
}
