#include <bits/stdc++.h>
using namespace std;
signed main() {
  int n;
  cin >> n;
  long long a[n];
  for (int i = 0; i < (n); ++i) cin >> a[i];
  int cnt = 0;
  for (int i = 0; i < n - 1; i++) {
    if (a[i] < a[i + 1]) {
      int step = a[i + 1] - a[i];
      cnt = cnt + step;
    }
  }
  cout << cnt << endl;
  return 0;
}
