#include <bits/stdc++.h>

using namespace std;
using i64 = long long;

constexpr int dx[] = {-1, 0, 0, 1}, dy[] = {0, -1, 1, 0};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  vector<string> g(n);
  for (int i = 0; i < n; ++i) {
    cin >> g[i];
  } 
  vector<vector<int>> vis(n, vector<int> (n, 1E9));  

  auto check = [&](int a, int b, int d) {
    if (a < 0 || a >= n || b < 0 || b >= n) return false;
    if (g[a][b] == '*') return false;
    if (d + 1 >= vis[a][b]) return false;
    return true;
  };

  auto bfs = [&]() {
    vis[0][0] = 0;
    queue<pair<int, int>> q;
    q.push({0, 0});
    while (q.size()) {
      auto [x, y] = q.front();
      q.pop();
      if (x == n - 1 && y == n - 1) {
        return vis[x][y];
      }
      int d = vis[x][y];
      for (int i = 0; i < 4; ++i) {
        int a = x + dx[i], b = y + dy[i];
        if (!check(a, b, d)) continue;
        vis[a][b] = d + 1;
        q.push({a, b});
      }
      for (int i = 1; i <= k; ++i) {
        if (i & 1) {
          int a = y + i / 2 + 1, b = x + i / 2;
          if (!check(a, b, d)) continue;
          vis[a][b] = d + 1;
          q.push({a, b});
        } else {
          int a = x + i / 2, b = y + i / 2;
          if (!check(a, b, d)) continue;
          vis[a][b] = d + 1;
          q.push({a, b});
        }
      }
    }
    return -1;
  };

  cout << bfs() << "\n";
  return 0;
}