#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=5005,INF=1<<29;

// https://www.dropbox.com/s/1zxohqaxrb87uft/Gifted_Infants_The_University_of_Tokyo___erated_files-job_14.pdf?dl=0

using uint = unsigned int ; using ll = long long ; using ull = unsigned long long ; template < class T > using V = vector <T>; template < class T > using VV = V <V<T>>;

int popcnt ( uint x ) { return __builtin_popcount(x); } int popcnt ( ull x ) { return __builtin_popcountll(x); } int bsr ( uint x ) { return 31 - __builtin_clz(x); } int bsr ( ull x ) { return 63 - __builtin_clzll(x); } int bsf ( uint x ) { return __builtin_ctz(x); } int bsf ( ull x ) { return __builtin_ctzll(x); }

struct FastSet { static constexpr uint B = 64 ; int n, lg; VV<ull> seg; FastSet( int _n) : n(_n) { do { seg.push_back(V<ull>((_n + B - 1 ) / B)); _n = (_n + B - 1 ) / B; } while (_n > 1 ); lg = seg.size(); } bool operator []( int i) const { return (seg[ 0 ][i / B] >> (i % B) & 1 ) != 0 ; } void set ( int i) { for ( int h = 0 ; h < lg; h++) { seg[h][i / B] |= 1ULL << (i % B); i /= B; } } void reset ( int i) { for ( int h = 0 ; h < lg; h++) { seg[h][i / B] &= ~( 1ULL << (i % B)); if (seg[h][i / B]) break ; i /= B; } } int next ( int i) { for ( int h = 0 ; h < lg; h++) { if (i / B == seg[h].size()) break ; ull d = seg[h][i / B] >> (i % B); if (!d) { i = i / B + 1 ; continue ; }  i += bsf(d); for ( int g = h - 1 ; g >= 0 ; g--) { i *= B; i += bsf(seg[g][i / B]); } return i; } return n; }  int prev ( int i) { i--; for ( int h = 0 ; h < lg; h++) { if (i == -1 ) break ; ull d = seg[h][i / B] << ( 63 - i % 64 ); if (!d) { i = i / B - 1 ; continue ; }  i += bsr(d) - (B - 1 ); for ( int g = h - 1 ; g >= 0 ; g--) { i *= B; i += bsr(seg[g][i / B]); } return i; } return -1 ; } };

int dis[MAX][MAX];

vector<int> dh={0,1,0,-1},dw={1,0,-1,0};

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N,K;cin>>N>>K;
    vector<string> S(N);
    for(int i=0;i<N;i++) cin>>S[i];
    
    queue<pair<int,int>> Q;
    for(int i=0;i<MAX;i++) for(int j=0;j<MAX;j++) dis[i][j]=INF;
    
    vector<int> L(N+N+2),R(N+N+2);
    for(int w=0;w<N;w++) L[w-0+N]=0;
    for(int h=0;h<N;h++) L[h-0+N]=h;
    
    for(int w=0;w<N;w++) R[w-(N-1)+N]=N-1;
    for(int h=0;h<N;h++) R[(N-1)-h+N]=h;
    
    vector<FastSet> SE(N+N+2,N);
    for(int i=0;i<N;i++){
        for(int j=0;j<N;j++){
            if(S[i][j]=='.') SE[j-i+N].set(i);
        }
    }
    
    dis[0][0]=0;
    Q.push(mp(0,0));
    
    while(!Q.empty()){
        auto [h,w]=Q.front();Q.pop();
        int d=dis[h][w];
        if(h==N-1&&w==N-1){
            cout<<d<<endl;
            return 0;
        }
        for(int k=0;k<4;k++){
            int toh=h+dh[k],tow=w+dw[k];
            if(toh<0||toh>=N||tow<0||tow>=N) continue;
            if(S[toh][tow]=='*') continue;
            if(chmin(dis[toh][tow],dis[h][w]+1)){
                Q.push(mp(toh,tow));
                SE[tow-toh+N].reset(toh);
            }
        }
        int can1=(K+1)/2;
        int can2=K/2;
        
        {
            int sh=w+1,sw=h,now=sh;
            while(1){
                int x=SE[sw-sh+N].next(now);
                if(x==N||x>=sh+can1) break;
                dis[x][sw-sh+x]=d+1;
                Q.push(mp(x,sw-sh+x));
                SE[sw-sh+N].reset(x);
                now=x;
            }
        }
        {
            int sh=h+1,sw=w+1,now=sh;
            while(1){
                int x=SE[sw-sh+N].next(now);
                if(x==N||x>=sh+can2) break;
                dis[x][sw-sh+x]=d+1;
                Q.push(mp(x,sw-sh+x));
                SE[sw-sh+N].reset(x);
                now=x;
            }
        }
    }
    
    cout<<-1<<endl;
}