#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(pii t)
{
    int i = t.first, j = t.second;
	return i <= n && j <= n && i >= 1 && j >= 1;
}
void BFS()
{
	queue <pii> qu;
    dis[1][1] = 0;
	qu.emplace(1,1);
    while(!qu.empty())
    {
        auto t = qu.front();
        qu.pop();
        forn(i,0,3)
        {
            auto pt = pii(t.first + dx[i], t.second + dy[i]);
            if(check(pt) && ps[pt.first][pt.second] && dis[pt.first][pt.second] == -1)
            {
                dis[pt.first][pt.second] = dis[t.first][t.second] + 1;
                qu.push(pt);
            }
        }
        forn(i,1,k/2)
        {
            auto pt = pii(t.first + i, t.second + i);
            if(check(pt)&& ps[pt.first][pt.second] && dis[pt.first][pt.second] == -1)
            {
                dis[pt.first][pt.second] = dis[t.first][t.second] + 1;
                if(ps[pt.first][pt.second]) qu.push(pt);
            }
            else break;
        }
        forn(i,1,(k + 1)/2)
        {
            auto pt = pii(t.second + i,t.first + i-1);
            if(check(pt)&& ps[pt.first][pt.second] && dis[pt.first][pt.second] == -1)
            {
                dis[pt.first][pt.second] = dis[t.first][t.second] + 1;
                qu.push(pt);
            }
            else if(k == 1)
            {
                continue;
            }else break;
        }
    }
}
#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();
    }
	BFS();
    printf("%d", dis[n][n]);
	return 0;
}