#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, n, d, x, step = 0;
  int a[2005];
  cin >> n >> d >> a[0];
  for (i = 1; i < n; i++) {
    cin >> a[i];
    x = (a[i - 1] - a[i]) / d;
    if (a[i] + x * d <= a[i - 1]) x++;
    if (x < 0) x = 0;
    a[i] += d * x;
    step += x;
  }
  cout << step << endl;
  return 0;
}
