#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  int sum = 0;
  int arr[N];
  for (int i = 0; i < N; i++) {
    cin >> arr[i];
  }
  for (int i = 0; i < N; i++) {
    int j = i + 1;
    while (j < N) {
      if (arr[i] > arr[j]) {
        sum += arr[i] - arr[j];
        j++;
      } else {
        break;
      }
    }
    if (arr[i] == *max_element(arr, arr + N - 1)) {
      break;
    }
  }
  cout << sum;
  return 0;
}
