#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>

using namespace std;
const int N = 310;
typedef pair<pair<int, int>, int> PII;
#define x first
#define y second

char g[N][N];
bool st[N][N];
int n, k;

bool check(int x, int y, int time)
{
    int t = 0;
    if (time < k)
    {
        t = 2;
    }
    else if (time > k && time < 2 * k)
    {
        t = 1;
    }
    if (x - t < 1 || x + t > n || y - t < 1 || y + t > n || st[x][y])
    {
        return false;
    }
    for (int i = x - t; i <= x + t; i++)
    {
        for (int j = y - t; j <= y + t; j++)
        {
            if (g[i][j] == '*')
            {
                return false;
            }
        }
    }

    return true;

}
int bfs()
{
    queue<PII>q;
    q.push({ {3, 3}, 0 });
    st[3][3] = true;

    int dx[4] = { 0,1,-1,0 }, dy[4] = { 1,0,0,-1 };
    while (q.size())
    {
        PII f = q.front();

        q.pop();
        if (f.y < 2 * k)
        {
            q.push({ {f.x.x,f.x.y},f.y + 1 });
        }
        if (f.x.x == n - 2 && f.x.y == n - 2)
        {
            return f.y;
        }
        for (int i = 0; i < 4; i++)
        {
            int nx = f.x.x + dx[i];
            int ny = f.x.y + dy[i];
            if (!check(nx, ny, f.y))
            {
                continue;
            }
            q.push({ {nx,ny}, f.y + 1 });
            st[nx][ny] = true;
        }
    }
    return -1;
}
int main()
{

    cin >> n >> k;
    for (int i = 1; i <= n; i++) cin >> g[i] + 1;
    cout << bfs() << endl;
    return 0;
}