#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n + 1], b[n + 1];
  for (int i = 1; i <= n; i++) cin >> a[i];
  b[1] = a[1];
  for (int i = 2; i <= n; i++) {
    if (a[i] >= a[i - 1]) {
      b[i] = a[i];
    } else
      b[i] = b[i - 1];
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) ans += b[i] - a[i];
  cout << ans << '\n';
  return 0;
}
