#include<bits/stdc++.h>
using namespace std;
#define rep(i,x,y) for (int i=(x);i<=(y);i++)
#define drep(i,y,x) for (int i=(y);i>=(x);i--)
#define pii pair<int,int>
#define fir first
#define sec second
#define MP make_pair
#define templ template<typename T>
templ bool chkmin(T &x,T y){return x>y?x=y,1:0;}
templ bool chkmax(T &x,T y){return x<y?x=y,1:0;}
void file() {
    #ifdef zqj
    freopen("a.in","r",stdin);
    #endif
}
typedef long long ll;
#define sz 5555


int n,K;
char s[sz][sz];
int vis[sz][sz];

int in(int x,int y){return x&&y&&x<=n&&y<=n&&s[x][y]!='*';}

pii fa[sz][sz]; int dis[sz][sz];
pii getfa(pii t) {
    if (!vis[t.fir][t.sec]||fa[t.fir][t.sec]==t) return t;
    if (getfa(fa[t.fir][t.sec])==fa[t.fir][t.sec]) return fa[t.fir][t.sec];
    dis[t.fir][t.sec]+=dis[fa[t.fir][t.sec].fir][fa[t.fir][t.sec].sec];
    return fa[t.fir][t.sec]=getfa(fa[t.fir][t.sec]);
}

int main() {
    file();
    ios::sync_with_stdio(false),cin.tie(0);
    scanf("%d %d",&n,&K);
    rep(i,1,n) scanf("%s",s[i]+1);
    vis[1][1]=1;
    rep(i,1,n) rep(j,1,n) if (in(i,j)) {
        int x=j+1,y=i,cc=1;
        while (!in(x,y)&&min(x,y)<=n&&cc<K) swap(x,y),++x,++cc;
        if (in(x,y)) fa[i][j]=pii{x,y},dis[i][j]=cc;
        else fa[i][j]=pii{i,j},dis[i][j]=0;
    }
    queue<pii>q;
    q.push({1,1});
    static int fx[4][2]={{1,0},{-1,0},{0,1},{0,-1}};
    while (q.size()) {
        auto [x,y]=q.front(); q.pop();
        if (x==n&&y==n) return cout<<vis[x][y]-1<<'\n',0;
        rep(i,0,3) {
            int xx=x+fx[i][0],yy=y+fx[i][1];
            if (in(xx,yy)&&!vis[xx][yy]) vis[xx][yy]=vis[x][y]+1,q.push({xx,yy});
        }
        while (getfa({x,y})!=pii{x,y}&&!vis[fa[x][y].fir][fa[x][y].sec]&&dis[x][y]<=K) {
            auto [xx,yy]=fa[x][y];
            vis[xx][yy]=vis[x][y]+1,q.push({xx,yy});
        }
    }
    cout<<-1<<'\n';
    return 0;
}