#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  int sum = 0;
  int maxi = a[0];
  for (int i = 1; i < n; ++i) {
    if (a[i] > maxi) {
      maxi = a[i];
    } else
      sum += abs(maxi - a[i]);
  }
  cout << sum;
}
