#include <bits/stdc++.h>
using namespace std;
int main() {
  long n, d, a[100000], diff;
  long sum = 0;
  cin >> n >> d;
  for (long i = 0; i < n; i++) cin >> a[i];
  for (long i = 1; i < n; i++) {
    if (a[i - 1] >= a[i]) {
      diff = a[i - 1] - a[i];
      a[i] = a[i] + (diff / d + 1) * d;
      sum = sum + diff / d + 1;
    }
  }
  cout << sum;
  return 0;
}
