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