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