#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int maxm = 0, ans = 0;
  for (int i = 0; i < n; ++i) {
    int x;
    cin >> x;
    maxm = max(x, maxm);
    ans += (maxm - x);
  }
  cout << ans;
  return 0;
}
