#include <bits/stdc++.h>
using namespace std;
long long a[100500];
int d;
int n;
long long ans = 0;
int main() {
  scanf("%d %d", &n, &d);
  for (int i = 0; i < n; i++) {
    int x;
    scanf("%d", &x);
    a[i] = x;
  }
  long long prev = -(1 << 30);
  for (int i = 0; i < n; i++) {
    if (a[i] <= prev) {
      long long dist = (prev + 1 - a[i]);
      long long cnt = (dist + d - 1) / d;
      ans += cnt;
      prev = a[i] + cnt * d;
    } else {
      prev = a[i];
    }
  }
  printf("%d", ans);
  return 0;
}
