#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];
  }
  long long ans = 0;
  int MaxNum = 0;
  for (int i = 1; i < n; i++) {
    MaxNum = max(MaxNum, arr[i]);
    int B = MaxNum;
    ans += B - arr[i];
  }
  cout << ans << "\n";
}
