/*
Optimal O(n^2) solution to Jumping Haybales.

*/


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

public class haybales_font
{
   public static void main(String[] args) throws Exception
   {
      PrintWriter out = new PrintWriter(System.out);
      new haybales_font(new FastScanner(System.in), out);
      out.close();
   }
   
   int n, k, oo = 987654321;

   public haybales_font(FastScanner in, PrintWriter out)
   {
      n = in.nextInt();
      k = in.nextInt();

      int[][] dp = new int[n][n];
      for (int[] dd : dp)
         Arrays.fill(dd, oo);
  
      MinQueue rowQueue = new MinQueue();
      MinQueue[] colQueue = new MinQueue[n];
      for (int i=0; i<n; i++)
         colQueue[i] = new MinQueue();

      dp[0][0] = 0;
      for (int i=0; i<n; i++)
      {
         rowQueue.clear();

         String s = in.next();
         for (int j=0; j<n; j++)
         {
            if (rowQueue.size() > k)
               rowQueue.poll();

            if (colQueue[j].size() > k)
               colQueue[j].poll();

            char c = s.charAt(j);
            if (c != '#')
            {
               dp[i][j] = Math.min(dp[i][j], rowQueue.minValue()+1);
               dp[i][j] = Math.min(dp[i][j], colQueue[j].minValue()+1);
            }

            rowQueue.add(dp[i][j]);
            colQueue[j].add(dp[i][j]);
         }
      }

      out.printf("%d%n", dp[n-1][n-1] == oo ? -1 : dp[n-1][n-1]);
   }
}


class MinQueue
{
   ArrayDeque<Integer> realQueue;
   ArrayDeque<Integer> minDeque;

   MinQueue()
   {
      realQueue = new ArrayDeque<>();
      minDeque = new ArrayDeque<>();
   }

   void clear()
   {
      realQueue.clear();
      minDeque.clear();
   }

   int size()
   {
      return realQueue.size();
   }

   void add(int v)
   {
      // Maintain the value for the real queue
      realQueue.addLast(v); 

      // Maintain the gradient for the smallest values possible.
      while (minDeque.size() > 0 && minDeque.peekLast().intValue() > v)
         minDeque.pollLast();  
      minDeque.addLast(v);
   }

   int poll()
   {
      int result = realQueue.pollFirst();
      if (minDeque.peekFirst().intValue() == result)
         minDeque.pollFirst();
   
      return result;
   }

   int minValue()
   {
      // Large value on failure.
      if (realQueue.size() == 0)
         return 987654321;
   
      return minDeque.peekFirst();
   }
}

class FastScanner{
    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    
    public FastScanner(InputStream stream)
    {
        this.stream = stream;
    }
    
    int read()
    {
        if (numChars == -1)
            throw new InputMismatchException();
        if (curChar >= numChars){
            curChar = 0;
            try{
                numChars = stream.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (numChars <= 0)
                return -1;
        }
        return buf[curChar++];
    }
    
    boolean isSpaceChar(int c)
    {
        return c==' '||c=='\n'||c=='\r'||c=='\t'||c==-1;
    }
    
    boolean isEndline(int c)
    {
        return c=='\n'||c=='\r'||c==-1;
    }
    
    int nextInt()
    {
        return Integer.parseInt(next());
    }
    
    long nextLong()
    {
        return Long.parseLong(next());
    }
    
    double nextDouble()
    {
        return Double.parseDouble(next());
    }
    
    String next(){
        int c = read();
        while (isSpaceChar(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = read();
        }while(!isSpaceChar(c));
        return res.toString();
    }
    
    String nextLine(){
        int c = read();
        while (isEndline(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = read();
        }while(!isEndline(c));
        return res.toString();
    }
}