#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, d, moves = 0;
  int* b;
  cin >> n >> d;
  b = new int[n];
  cin >> b[0];
  for (int i = 1; i < n; i++) {
    cin >> b[i];
    if (b[i] <= b[i - 1]) {
      int time = (b[i - 1] - b[i]) / d + 1;
      b[i] += time * d;
      moves += time;
    }
  }
  delete[] b;
  cout << moves;
}
