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