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