#include <bits/stdc++.h>
using namespace std;
const double diff = pow(10, -6);
int d;
void solve() {
  int n, ans = 0;
  cin >> n;
  int a[n];
  for (int i = 0; i < (n); i++) cin >> a[i];
  for (int i = 0; i < (n - 1); i++) {
    if (a[i + 1] > a[i]) ans += a[i + 1] - a[i];
  }
  cout << ans;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t = 1;
  while (t--) solve();
}
