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