A sequence a0, a1, ..., at - 1 is called increasing if ai - 1 < ai for each i: 0 < i < t.

You are given a sequence b0, b1, ..., bn - 1 and a positive integer d. In each move you may choose one element of the given sequence and add d to it. What is the least number of moves required to make the given sequence increasing?

Input

The first line of the input contains two integer numbers n and d (2 ≤ n ≤ 2000, 1 ≤ d ≤ 106). The second line contains space separated sequence b0, b1, ..., bn - 1 (1 ≤ bi ≤ 106).

Output

Output the minimal number of moves needed to make the sequence increasing.

Examples

Input

4 2
1 3 3 2


Output

3
import java.util.*;
import java.io.*;
import java.math.BigInteger;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		InputReader in = new InputReader(new InputStreamReader(System.in));
		PrintWriter out = new PrintWriter(System.out);
		new Task().go(in, out);
		out.close();
	}

}

class Task {
	public int maxn = 2010;
	long [] b = new long[maxn];
	int n, d;
	public void go(InputReader in, PrintWriter out) {
		n = in.nextInt(); d = in.nextInt();
		for(int i=0; i<n; i++) b[i] = in.nextLong();
		long ans = 0;
		for(int i=1; i<n; i++) {
			if(b[i]>b[i-1]) continue;
			long tmp = (b[i-1] - b[i])/d + 1;
			ans += tmp;
			b[i] += tmp * (long)d;
		}
		out.println(ans);
	}
}

class InputReader {
	BufferedReader bf;
	StringTokenizer st;

	InputReader(InputStreamReader is) {
		bf = new BufferedReader(is);
	}

	public String next() {
		if (st == null || !st.hasMoreElements()) {
			try {
				st = new StringTokenizer(bf.readLine());
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		return st.nextToken();
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public long nextLong() {
		return Long.parseLong(next());
	}

	public double nextDouble() {
		return Double.parseDouble(next());
	}
}

	  	     	 	 	 	     	 	 	  		