#include <bits/stdc++.h>
using namespace std;
int v[2009];
int main() {
  int n, d, ans = 0, t;
  scanf("%d%d%d", &n, &d, &v[0]);
  for (int i = 1; i < n; i++) {
    scanf("%d", &v[i]);
    if (v[i - 1] >= v[i]) {
      t = ceil((double)(v[i - 1] + 1 - v[i]) / (double)d);
      ans += t;
      v[i] += t * d;
    }
  }
  printf("%d\n", ans);
  return 0;
}
