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