#include <bits/stdc++.h>
using namespace std;
int n,d,a[2001],ans;
int main(){
	scanf("%d%d",&n,&d);
	a[0] = -0x3f;
	for(int i = 1;i<=n;i++){
		scanf("%d",&a[i]);
		while(a[i]<=a[i-1]){
			a[i]+=d;
			ans++;
		}
	}
	printf("%d",ans);
	return 0;
}