#include <bits/stdc++.h>
using namespace std;
long long int arr[1000000];
int main() {
  int n;
  cin >> n;
  long long int count = 0;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  long long int Min = arr[0];
  long long int Max = arr[0];
  for (int i = 1; i < n; i++) {
    if (arr[i] >= arr[i - 1])
      Min = Max = arr[i];
    else {
      int j = i;
      long long int mmin = arr[j - 1];
      long long int mmax = arr[j - 1];
      int c = 0;
      while (arr[j - 1] > arr[j]) {
        mmin = min(arr[j], mmin);
        mmax = max(arr[j], mmax);
        j++;
        if (j == n) break;
        c++;
      }
      count += mmax - mmin;
      i += c;
    }
  }
  cout << count << endl;
  return 0;
}
