#include<bits/stdc++.h>

using namespace std;
#define forn(i,p,q) for(long long i = p;i <=q;i++)
long long read()
{
 	long long t;
 	cin >> t;
  	return t;
}
#define all(p) p.begin(),p.end()
const int N = 5005;
#define pii pair<int,int>
set <int> st[2 * N];
int dis[N][N];
int dx[] = {1,-1,0,0};
int dy[] = {0,0,1,-1};
int n, k;
bool ps[N][N];
inline bool check(int i,int j)
{
	return i <= n && j <= n && i >= 1 && j >= 1;
}
inline void ers(int i, int j)
{
	st[i-j+n].erase(i);
}
void BFS()
{
	queue <pii> qu;
	qu.emplace(1,1);
	ers(1,1);
	dis[1][1] = 0;
	while(!qu.empty())
	{
		auto pt = qu.front();
		qu.pop();
        pii t;
		for(auto&& it = st[pt.first-pt.second + n].lower_bound(pt.first);it != st[pt.first-pt.second + n].end() && *it - pt.first <= k / 2;)
		{
            t.first = *it;
            t.second = t.first - pt.first + pt.second;
            ++it;
            dis[t.first][t.second] = dis[pt.first][pt.second] + 1;
            qu.emplace(t.first,t.second);
            ers(t.first,t.second);
		}
		for(auto && it = st[pt.second + 1 - pt.first + n].lower_bound(pt.second + 1);it != st[pt.second + 1 - pt.first + n].end() && *it - pt.second <= (k + 1) / 2;)
		{
            t.first = *it;
            t.second = t.first - pt.second + pt.first - 1;
            ++it;
            dis[t.first][t.second] = dis[pt.first][pt.second] + 1;
            qu.emplace(t.first,t.second);
            ers(t.first,t.second);
		}
		forn(i,0,3)
		{
			t.first  = pt.first + dx[i];
            t.second = pt.second + dy[i];
			if(check(t.first, t.second) && dis[t.first][t.second] == -1 && ps[t.first][t.second])
			{
				dis[t.first][t.second] = dis[pt.first][pt.second] + 1;
				qu.emplace(t.first,t.second);
				ers(t.first,t.second);
			}
		}
        if(dis[n][n] != -1) return ;
	}
}
#define FAST ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
int main()
{
    scanf("%d %d\n", &n, &k);
	memset(dis,-1,sizeof(dis));
	forn(i,1,n)
    {
        forn(j,1,n)
        {
            ps[i][j] = getchar() == '.';
        }
        getchar();
    }
	forn(i,1,n)
	{
		forn(j,1,n)
		{
            if(ps[i][j]) st[i-j+n].emplace(i);
		}
	}
	BFS();
    printf("%d", dis[n][n]);
	return 0;
}