#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) {
    int n, ans = 0;
    cin >> n;
    int a[n], b[n];
    for (int i = 0; i < n; i++) {
      cin >> a[i];
    }
    b[0] = 0;
    int tmpu = 0;
    for (int i = 1; i < n; i++) {
      int temp = a[tmpu] - a[i];
      if (temp > 0)
        b[i] = temp;
      else {
        b[i] = 0;
        tmpu = i;
      }
    }
    for (int i = 0; i < n; i++) ans += b[i];
    cout << ans;
  }
  return 0;
}
