#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef basic_string<int> BI;
typedef long long ll;
typedef pair<int,int> PII;
typedef double db;
mt19937 mrand(random_device{}()); 
const ll mod=998244353;
int rnd(int x) { return mrand() % x;}
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;}
// head

const int N=5010,M=N*N;
int n,k,f[M],dis[M];
char s[N][N];
vector<PII> dir{{-1,0},{1,0},{0,-1},{0,1}};
int find(int x) {
	return f[x]==x?x:f[x]=find(f[x]);
}
void del(int fx,int fy) {
	assert(fx<n&&fy<n);
	f[find(fx*(n+1)+fy)]=find((fx+1)*(n+1)+(fy+1));
}
PII getx(int fx,int fy) {
	int id=find(fx*(n+1)+fy);
	return mp(id/(n+1),id%(n+1));
}
int main() {
	scanf("%d%d",&n,&k);
	rep(i,0,n) scanf("%s",s[i]);
	rep(i,0,n+1) rep(j,0,n+1) f[i*(n+1)+j]=i*(n+1)+j;
	rep(i,0,n*n) dis[i]=n*n+1;
	rep(i,0,n) rep(j,0,n) if (s[i][j]=='*') {
		del(i,j);
	}
	dis[0]=0;
	queue<PII> q;
	q.push(mp(0,0));
	del(0,0);
	while (!q.empty()) {
		auto [x,y]=q.front();
		q.pop();
		for (auto [dx,dy]:dir) {
			int nx=x+dx,ny=y+dy;
			if (nx>=0&&nx<n&&ny>=0&&ny<n&&dis[nx*n+ny]>dis[x*n+y]+1&&
				s[nx][ny]!='*') {
				dis[nx*n+ny]=dis[x*n+y]+1;
				q.push(mp(nx,ny));
				del(nx,ny);
			}
		}
		while (1) {
			auto [fx,fy]=getx(x,y);
			if (fx>=n||fy>=n||(fx-x)*2>k) break;
			dis[fx*n+fy]=dis[x*n+y]+1;
			q.push(mp(fx,fy));
			del(fx,fy);
		}
		while (1) {
			auto [fx,fy]=getx(y+1,x);
			if (fx>=n||fy>=n||(fy-x)*2+1>k) break;
			dis[fx*n+fy]=dis[x*n+y]+1;
			q.push(mp(fx,fy));
			del(fx,fy);
		}
	}
	int ans=dis[n*n-1];
	if (ans>=n*n) ans=-1;
	printf("%d\n",ans);
}