#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, T, x, y, syc = 0;
  cin >> N >> T;
  cin >> x;
  for (int i = 2; i <= N; i++) {
    cin >> y;
    if (x >= y) {
      syc += (x - y) / T + 1;
      x = y + ((x - y) / T + 1) * T;
    } else
      x = y;
  }
  cout << syc << endl;
  return 0;
}
