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