#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false), cin.tie(0);
  int n, d, num, nextNum, ans = 0;
  cin >> n >> d;
  cin >> num;
  for (int i = 1; i < n; i++) {
    cin >> nextNum;
    if (nextNum < num) {
      ans += ceil(((double)num - nextNum) / d);
      nextNum = nextNum + d * ceil(((double)num - nextNum) / d);
    }
    if (num == nextNum) {
      nextNum = nextNum + d;
      ans++;
    }
    num = nextNum;
  }
  cout << ans << "\n";
  return 0;
}
