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