#include <bits/stdc++.h>
using namespace std;
int a[2005];
int main() {
  int n, d;
  scanf("%d%d", &n, &d);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    if (a[i - 1] >= a[i]) {
      int tmp = a[i - 1] - a[i];
      a[i] += ((tmp / d) + 1) * d;
      ans++;
      ans += tmp / d;
    }
  }
  cout << ans << endl;
  return 0;
}
