#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  int ans = 0;
  for (int i = 1; i < n; i++) {
    ans += max((arr[i] - arr[i - 1]), 0);
  }
  cout << ans;
}
