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