#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n;
  cin >> n;
  long long int a[n];
  for (long long int i = 0; i < n; i++) cin >> a[i];
  long long int sum = 0;
  for (long long int i = 1; i < n - 1; i++) {
    sum += max(a[i] - a[i - 1], (long long int)0);
  }
  cout << sum << "\n";
}
