#include <bits/stdc++.h>
using namespace std;
int n, ans, mx;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 0, h; i < n; ++i) {
    cin >> h;
    mx = max(h, mx);
    ans += mx - h;
  }
  cout << ans;
}
