#include <iostream>
#include <queue>
using namespace std;
const int N=305;
int n,k;
char g[N][N];
bool st[N][N];
int dx[4]= {0,1,0,-1};
int dy[4]= {1,0,-1,0};
int d[3]= {2,1,0};
struct Edge
{
    int x;
    int y;
    int time;
    Edge(int x,int y,int time)
    {
        this->x=x;
        this->y=y;
        this->time=time;
    }
};
//三维 bfs
int bfs()
{
    queue<Edge> q;
    //Edge e=Edge(3,3,0);
    q.push(Edge(3,3,0));
    st[3][3]=true;

    while(!q.empty())
    {
        //将原点加入队列，即静止不动

        Edge t=q.front();
        q.pop();
        if(t.time/k<2)
            q.push(Edge(t.x,t.y,t.time+1));

        for(int i=0; i<4; i++)
        {
            int a=t.x+dx[i];
            int b=t.y+dy[i];

            int fat=t.time/k>=2?0:d[t.time/k];//有多胖
            if(a-fat<=0||a+fat>n||b-fat<=0||b+fat>n)
                continue;//弱国超出迷宫界限
            if(st[a][b])
                continue;

            //判断所占区域是否有障碍物

            bool flag=false;
            for(int u=a-fat; u<=a+fat; u++)
            {
                for(int v=b-fat; v<=b+fat; v++)
                {
                    if(g[u][v]=='*')
                        flag=true;
                }
            }
            if(flag)
                continue;

            if(a==n-2&&b==n-2)
                return t.time+1;
            st[a][b]=true;
            //加入队列
            q.push(Edge(a,b,t.time+1));
        }
    }

}
int main()
{
    cin>>n>>k;
    for(int i=0; i<n; i++)
    {
        string s;
        cin>>s;
        for(int j=0; j<s.size(); j++)
        {
            g[i+1][j+1]=s[j];
        }
    }

    cout<<bfs();

    return 0;
}