#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int cnt = 0;
  int previous = 0;
  for (int i = 1; i <= n; i++) {
    int height;
    cin >> height;
    if (height < previous) {
      cnt += previous - height;
      height = previous;
    }
    previous = height;
  }
  cout << cnt << endl;
}
