#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];
  if (n == 1) {
    cout << 0 << endl;
    return 0;
  }
  int cnt = 0;
  for (int i = 0; i < n - 1; i++) {
    cnt += max(a[i + 1] - a[i], 0);
  }
  cout << cnt << endl;
}
