#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  vector<int> a(N);
  int v = 0;
  for (int i = 0; i < N; i++) {
    cin >> a[i];
  }
  int maxx = a[0];
  for (int i = 1; i < N; i++) {
    maxx = max(maxx, a[i]);
    if (maxx != a[i]) {
      v += abs(maxx - a[i]);
    }
  }
  cout << v << endl;
  return 0;
}
