#include<bits/stdc++.h>
using namespace std;

using pii=pair<int,int>;

const int N=5e3+1e2+7;

int n,k;

char s[N][N];

queue<pii>q;

int fa[N*2][N];

int d[N][N];

int find(int d,int x)
{
    return fa[d][x]==x?x:fa[d][x]=find(d,fa[d][x]);
}

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

int main()
{
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)
        scanf("%s",s[i]+1);
    for(int i=1;i<=n+1;i++)
    {
        for(int j=1;j<=n+1;j++)
            fa[i-j+n][i]=i;
    }
    memset(d,-1,sizeof(d));
    q.push({1,1});
    d[1][1]=0;
    fa[0+n][1]=2;
    while(!q.empty())
    {
        auto [x,y]=q.front();
        q.pop();
        if(s[x][y]=='*')
            continue;
        for(int t=0;t<4;t++)
        {
            int tx=x+dx[t],ty=y+dy[t];
            if(tx<1||tx>n||ty<1||ty>n||d[tx][ty]!=-1)
                continue;
            d[tx][ty]=d[x][y]+1;
            fa[tx-ty+n][tx]=tx+1;
            q.push({tx,ty});
        }
        int c=k/2;
        for(int i=find(x-y+n,x);i<=x+c;i=find(x-y+n,i))
        {
            if(i>n||y+i-x>n)
                break;
            d[i][y+i-x]=d[x][y]+1;
            q.push({i,y+i-x});
            fa[x-y+n][i]=i+1;
        }
        c=k-c-1;
        for(int i=find(y+1-x+n,y+1);i<=n&&i<=y+1+c;i=find(y+1-x+n,i))
        {
            if(i>n||x-(y+1)+i>n)
                break;
            d[i][x-(y+1)+i]=d[x][y]+1;
            q.push({i,x-(y+1)+i});
            fa[(y+1)-x+n][i]=i+1;
        }
    }
    printf("%d\n",d[n][n]);
}