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.io.*;
import java.util.*;

public class A implements Runnable {
	public static void main(String[] args) {
		new A().run();
	}

	class FastScanner {
		BufferedReader br;
		StringTokenizer st;
		boolean eof;
		String buf;

		public FastScanner(String fileName) throws FileNotFoundException {
			br = new BufferedReader(new FileReader(fileName));
			nextToken();
		}

		public FastScanner(InputStream stream) {
			br = new BufferedReader(new InputStreamReader(stream));
			nextToken();
		}

		String nextToken() {
			while (st == null || !st.hasMoreTokens()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (Exception e) {
					eof = true;
					break;
				}
			}
			String ret = buf;
			buf = eof ? "-1" : st.nextToken();
			return ret;
		}

		int nextInt() {
			return Integer.parseInt(nextToken());
		}

		long nextLong() {
			return Long.parseLong(nextToken());
		}

		double nextDouble() {
			return Double.parseDouble(nextToken());
		}

		void close() {
			try {
				br.close();
			} catch (Exception e) {

			}
		}

		boolean isEOF() {
			return eof;
		}
	}

	FastScanner sc;
	PrintWriter out;

	public void run() {
		Locale.setDefault(Locale.US);
		try {
			sc = new FastScanner(System.in);
			out = new PrintWriter(System.out);
			solve();
			sc.close();
			out.close();
		} catch (Throwable e) {
			e.printStackTrace();
			System.exit(1);
		}
	}

	int nextInt() {
		return sc.nextInt();
	}

	String nextToken() {
		return sc.nextToken();
	}

	long nextLong() {
		return sc.nextLong();
	}

	double nextDouble() {
		return sc.nextDouble();
	}

	void solve() {
		int n = nextInt();
		int d = nextInt();
		long last = Integer.MIN_VALUE;
		long ans = 0;
		for (int i = 0; i < n; i++) {
			long x = nextInt();
			if (x <= last) {
				long dif = last + 1 - x;
				x += (dif + d - 1) / d * d;
				ans += (dif + d - 1) / d;
				last = x;
			} else {
				last = x;
			}
		}
		out.println(ans);
	}
}