#include<bits/stdc++.h>

using lint = int64_t;
using namespace std;

int main(void) {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n, k;
  cin>>n>>k;
  vector<string>s(n);
  for(int i=0;i<n;i++) cin>>s[i];
  vector<pair<int, int>>cur;
  vector<vector<int>>dist(n, vector<int>(n, -1));
  dist[0][0] = 0;
  cur.push_back({0, 0});
  vector<int>dx = {0, 1, 0, -1};
  vector<int>dy = {1, 0, -1, 0};
  
  while(!cur.empty()){
    vector<pair<int, int>>nxt;
    sort(cur.begin(), cur.end(), [&](pair<int, int>a, pair<int, int>b){
      return a.first + a.second > b.first + b.second;
    });
    for(auto [a, b] : cur){
      for(int i=2;i<=k;i+=2){
        int na = a + i/2, nb = b + i/2;
        if(na < 0 || na >= n || nb < 0 || nb >= n || s[na][nb] == '*') continue;
        if(dist[na][nb] != -1) break;
        dist[na][nb] = dist[a][b] + 1;
        nxt.push_back({na, nb});
      }
      for(int i=1;i<=k;i+=2){
        int na = b + 1 + i/2, nb = a + i / 2;
        if(na < 0 || na >= n || nb < 0 || nb >= n || s[na][nb] == '*') continue;
        if(dist[na][nb] != -1) break;
        dist[na][nb] = dist[a][b] + 1;
        nxt.push_back({na, nb});
      }
    }
    for(auto [a, b] : cur){
      for(int k=0;k<4;k++){
        int na = a + dx[k], nb = b + dy[k];
        if(na < 0 || na >= n || nb < 0 || nb >= n || s[na][nb] == '*' || dist[na][nb] != -1) continue;
        dist[na][nb] = dist[a][b] + 1;
        nxt.push_back({na, nb});
      }
    }
    swap(nxt, cur);
  }
  cout<<dist[n-1][n-1]<<"\n";

  return 0;
}