#include <bits/stdc++.h>
using namespace std;
long long s[1000005];
int main(void) {
  int n, d, ans = 0;
  cin >> n >> d >> s[1];
  for (int i = 2; i <= n; ++i) {
    cin >> s[i];
    int cnt = 0;
    if (s[i] <= s[i - 1]) cnt = (s[i - 1] - s[i] + d) / d;
    s[i] += cnt * d;
    ans += cnt;
  }
  return cout << ans << '\n', 0;
}
