#include <bits/stdc++.h>
int a[2010];
int main(void) {
  int n, d, ans = 0;
  scanf("%d%d", &n, &d);
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }
  for (int i = 1; i < n; i++) {
    if (a[i] <= a[i - 1]) {
      int t = a[i - 1] - a[i];
      if ((t + 1) % d == 0) {
        a[i] += t + 1;
        ans += (t + 1) / d;
      } else {
        a[i] += ((t + 1) / d + 1) * d;
        ans += (t + 1) / d + 1;
      }
    }
  }
  printf("%d\n", ans);
  return 0;
}
