#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  int bsum = accumulate(a.begin(), a.end(), 0);
  int la = a[0];
  for (int i = 1; i < n; i++) {
    if (a[i] < la) {
      a[i] = la;
    } else {
      la = a[i];
    }
  }
  int asum = accumulate(a.begin(), a.end(), 0);
  int sub = asum - bsum;
  cout << sub << endl;
  return 0;
}
