#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  int sum = 0;
  int max = 0;
  int x;
  for (int i = 0; i < n - 1; i++) {
    if (a[i] >= max) max = a[i];
    if (a[i + 1] >= max) {
      x = 0;
    } else {
      x = max - a[i + 1];
    }
    sum = sum + x;
  }
  cout << sum;
  return 0;
}
