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