#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int mx;
  cin >> mx;
  int answer = 0;
  for (int i = 1; i < n; i++) {
    int a;
    cin >> a;
    mx = max(mx, a);
    answer += mx - a;
  }
  cout << answer << endl;
}
