#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=l; i<=r; i++)
#define IOS {cin.tie(0);cout.tie(0);ios::sync_with_stdio(0);}
using namespace std;

typedef long long ll;
typedef pair<int,int> P;

char s[5050][5050];
vector<int> q[10010];
bool vis[5050][5050];
int n, top, visdig[10010];
P ksj[25000010];

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

int digs[10010], numdigs;

void mark(int x, int y, int k) {
    rep (i, 0, k-1) {
        int tx = x + i, ty = y + i;
        if (tx > n || ty > n) break;
        if (s[tx][ty] == '*') continue;
        if (vis[tx][ty]) break;
        vis[tx][ty] = 1;
        ksj[++top] = P(tx, ty);
    }
}

bool cmp(int a, int b) {
    return a > b;
}

int main() {
    int k;
    scanf("%d%d", &n, &k);
    rep (i, 1, n) {
        scanf("%s", s[i]+1);
    }
    q[2].push_back(1);
    vis[1][1] = 1;
    digs[++numdigs] = 2;
    visdig[2] = 1;
    rep (d, 1, n*n) {
        rep (_, 1, numdigs) {
            int dig = digs[_];
            for (int i = 0; i < q[dig].size(); i++) {
                int x = q[dig][i], y = dig - x;
                mark(x+1, y+1, k/2);
                mark(y+1, x, (k+1)/2);
            }
        }
        rep (_, 1, numdigs) {
            int dig = digs[_];
            for (int i = 0; i < q[dig].size(); i++) {
                int x = q[dig][i], y = dig - x;
                rep (l, 0, 3) {
                    int tx = x + dx[l], ty = y + dy[l];
                    if (tx >= 1 && tx <= n && ty >= 1 && ty <= n && s[tx][ty] == '.' && !vis[tx][ty]) {
                        vis[tx][ty] = 1;
                        ksj[++top] = P(tx, ty);
                    }
                }
            }
        }
        rep (i, 1, numdigs) {
            q[digs[i]].clear();
            visdig[digs[i]] = 0;
        }
        numdigs = 0;
        rep (i, 1, top) {
            int x = ksj[i].first, y = ksj[i].second;
            q[x+y].push_back(x);
            if (!visdig[x+y]) visdig[x+y] = 1, digs[++numdigs] = x+y;
        }
        sort(digs+1, digs+numdigs+1, cmp);
        top = 0;
        if (vis[n][n]) {
            cout << d;
            return 0;
        }
        if (numdigs == 0) break;
    }
    cout <<-1;
    return 0;
}