#include <bits/stdc++.h>
using namespace std;
int A[200000];
int main() {
  int N, max_temp = 0, sum = 0;
  cin >> N;
  for (int i = 0; i < N; i++) {
    cin >> A[i];
  }
  for (int i = 0; i < N; i++) {
    if (max_temp < A[i]) {
      max_temp = A[i];
    } else if (max_temp >= A[i]) {
      sum += max_temp - A[i];
    }
  }
  cout << sum;
  return 0;
}
