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.*;

public class BasicJava 
{
   
   public static void main(String[] args)
   {
      Task Main = new Task();
      
      Main.solve();
   }
   
   public static class Task
   {
      InputReader in = new InputReader(System.in);
      PrintWriter out = new PrintWriter(System.out);
      
      public void solve()
      {
         int n = in.nextInt();
         int d = in.nextInt();
         
         long[] t = new long[2010];
         
         for (int i = 1; i <= n; i++) t[i] = in.nextLong();
         
         long ans = 0;
         
         for (int i = 2; i <= n; i++) 
            if (t[i] <= t[i - 1]){
            
            long x = (t[i - 1] - t[i]) / d + 1;
            
            ans = ans + x;
            
            t[i] = t[i] + 1L * d * x;
         }
         
         out.println(ans);
         
         out.close();
         
      }
   }

   static class InputReader
   {
      private InputStream stream;
      private byte[] buf = new byte[2048];
      private int curChar;
      private int numChars;
 
      public InputReader(InputStream stream)
      {
         this.stream = stream;
      }
 
      public int read()
      {
         if (numChars == -1)
            throw new UnknownError();
         if (curChar >= numChars)
         {
            curChar = 0;
            try
            {
               numChars = stream.read(buf);
            }
            catch (IOException e)
            {
               throw new UnknownError();
            }
            if (numChars <= 0)
               return -1;
         }
         return buf[curChar++];
      }
 
      public int peek()
      {
         if (numChars == -1)
            return -1;
         if (curChar >= numChars)
         {
            curChar = 0;
            try
            {
               numChars = stream.read(buf);
            }
            catch (IOException e)
            {
               return -1;
            }
            if (numChars <= 0)
               return -1;
         }
         return buf[curChar];
      }
 
      public void skip(int x)
      {
         while (x-- > 0)
            read();
      }
 
      public int nextInt()
      {
         return Integer.parseInt(next());
      }
 
      public long nextLong()
      {
         return Long.parseLong(next());
      }
 
      public String nextString()
      {
         return next();
      }
 
      public String next()
      {
         int c = read();
         while (isSpaceChar(c))
            c = read();
         StringBuffer res = new StringBuffer();
         do
         {
            res.appendCodePoint(c);
            c = read();
         }
         while (!isSpaceChar(c));
 
         return res.toString();
      }
 
      public String nextLine()
      {
         StringBuffer buf = new StringBuffer();
         int c = read();
         while (c != '\n' && c != -1)
         {
            if (c != '\r')
               buf.appendCodePoint(c);
            c = read();
         }
         return buf.toString();
      }
 
      public double nextDouble()
      {
         int c = read();
         while (isSpaceChar(c))
            c = read();
         int sgn = 1;
         if (c == '-')
         {
            sgn = -1;
            c = read();
         }
         double res = 0;
         while (!isSpaceChar(c) && c != '.')
         {
            if (c == 'e' || c == 'E')
               return res * Math.pow(10, nextInt());
            if (c < '0' || c > '9')
               throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
         }
         if (c == '.')
         {
            c = read();
            double m = 1;
            while (!isSpaceChar(c))
            {
               if (c == 'e' || c == 'E')
                  return res * Math.pow(10, nextInt());
               if (c < '0' || c > '9')
                  throw new InputMismatchException();
               m /= 10;
               res += (c - '0') * m;
               c = read();
            }
         }
         return res * sgn;
      }
 
      public boolean hasNext()
      {
         int value;
         while (isSpaceChar(value = peek()) && value != -1)
            read();
         return value != -1;
      }
 
      private boolean isSpaceChar(int c)
      {
         return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
      }
 
   }
}