#include <bits/stdc++.h>
int main() {
  int n, d, b0, b, moves(0);
  scanf("%d%d%d", &n, &d, &b0);
  while (--n) {
    scanf("%d", &b);
    if (b <= b0) {
      int x = (b0 - b) / d + 1;
      moves += x;
      b0 = b + x * d;
    } else {
      b0 = b;
    }
  }
  printf("%d\n", moves);
  return 0;
}
