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