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

//#define ONLINE
#ifndef ONLINE
#define debug(...) fprintf(stderr,##__VA_ARGS__)
#else
#define debug(...) ;
#endif

using LL=long long;
using PII=pair<int,int>;

template<typename T>
inline T READ(){
	T x=0; bool f=0; char c=getchar();
	while(c<'0' || c>'9') f|=(c=='-'),c=getchar();
	while(c>='0' && c<='9') x=x*10+c-'0',c=getchar();
	return f?-x:x;
}
inline int read(){return READ<int>();}
inline LL readLL(){return READ<LL>();}
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());

#define N 5010
int n,lim;
char g[N][N];

int fa[N*N],dis[N][N];
int G(int x){
	return x==fa[x]?x:fa[x]=G(fa[x]);
}

int dir[4][2]={{1,0},{-1,0},{0,1},{0,-1}};
int main(){
	n=read(),lim=read();
	for(int i=1;i<=n;i++){
		scanf("%s",g[i]+1);
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			fa[i*(n+1)+j]=i*(n+1)+j;
		}
	}
	queue<PII>p; p.push({1,1});
	memset(dis,-1,sizeof(dis)); dis[1][1]=0;
	while(p.size()){
		auto [x,y]=p.front(); p.pop();
		for(int i=0;i<4;i++){
			int nx=x+dir[i][0];
			int ny=y+dir[i][1];
			if(nx<1 || ny<1 || nx>n || ny>n || g[nx][ny]=='*') continue;
			if(dis[nx][ny]==-1){
				p.push({nx,ny});
				dis[nx][ny]=dis[x][y]+1;
			}
		}
		while(1){
			int h=G(x*(n+1)+y);
			int nx=h%(n+1)+1,ny=h/(n+1);//(nx,ny)=(y+1,x)
			if(nx<1 || ny<1 || nx>n || ny>n) break;
			if(nx+ny-(x+y)>lim) break;
			if(g[nx][ny]=='.' && dis[nx][ny]==-1){
				p.push({nx,ny});
				dis[nx][ny]=dis[x][y]+1;
			}
			fa[h]=nx*(n+1)+ny;
		}
	}
	printf("%d\n",dis[n][n]==INT_MAX?-1:dis[n][n]);
	return 0;
}

/* stuff you should look for
* int overflow, array bounds
* special cases (n=1?)
* do smth instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
*/