#include <bits/stdc++.h>

using namespace std;

#define x first
#define y second

typedef pair<int,int> PII;
const int N=5010;

int n,k;
PII fa[N][N];
PII q[N*N];
int dist[N][N];
char str[N][N];

int dx[4]={0,-1,0,1},dy[4]={-1,0,1,0};

PII find(int x,int y)
{
	if(fa[x][y]!=(PII){x,y}) fa[x][y]=find(fa[x][y].x,fa[x][y].y);
	return fa[x][y];
}

void merge(PII a,PII b)
{
	PII x=find(a.x,a.y),y=find(b.x,b.y);
	if(x!=y) fa[x.x][x.y]=y;
}

void bfs()
{
	int tt=-1,hh=0;
	memset(dist,-1,sizeof(dist));
	dist[1][1]=0;
	q[++tt]={1,1};
	while(hh<=tt){
		int x=q[hh].x,y=q[hh].y;++hh;
		
		for(int i=0;i<4;i++){
			int a=x+dx[i],b=y+dy[i];
			if(a<1 || a>n || b<1 || b>n || dist[a][b]!=-1 || str[a][b]=='*') continue;
			dist[a][b]=dist[x][y]+1;
			q[++tt]={a,b};
		}
		
		PII t=find(x,y);
		for(int a=t.x,b=t.y,i=t.x+t.y-x-y+1;i<=k;i++){
			swap(a,b);++a;
			if(a>n || b>n) break;
			merge(t,{a,b});
			if(find(a,b)!=(PII){a,b}) break;
			if(dist[a][b]!=-1) continue;
			if(str[a][b]=='*') continue;
			dist[a][b]=dist[x][y]+1;
			q[++tt]={a,b};
		}
	}
}

int main()
{
	scanf("%d%d",&n,&k);
	for(int i=1;i<=n;i++) scanf("%s",str[i]+1);
	for(int i=1;i<=n;i++)
		for(int j=1;j<=n;j++)
			fa[i][j]={i,j};
	
	bfs();
	printf("%d\n",dist[n][n]);
	
	return 0;
}