#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  vector<int> tall(N);
  int max = 0, total_step = 0;
  for (int i = 0; i < N; i++) {
    cin >> tall[i];
    if (max > tall[i]) {
      total_step += max - tall[i];
    }
    if (tall[i] > max) {
      max = tall[i];
    }
  }
  cout << total_step;
}
