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