#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, d, res = 0, a = 0, b;
  cin >> n >> d;
  for (int i = 0; i < n; i++) {
    cin >> b;
    if (a >= b) {
      res += ceil((a - b + 1) / (double)d);
      b += ceil((a - b + 1) / (double)d) * d;
    }
    a = b;
  }
  cout << res << endl;
}
