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