#include "bits/stdc++.h"

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep1(i, n) for (int i = 1; i < (n); ++i)
#define rep1n(i, n) for (int i = 1; i <= (n); ++i)
#define repr(i, n) for (int i = (n) - 1; i >= 0; --i)
#define pb push_back
#define eb emplace_back
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define each(x, a) for (auto &x : a)
#define ar array
#define vec vector
#define range(i, n) rep(i, n)

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using str = string;
using pi = pair<int, int>;
using pl = pair<ll, ll>;

using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pair<int, int>>;
using vvi = vector<vi>;

int Bit(int mask, int b) { return (mask >> b) & 1; }

template<class T>
bool ckmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool ckmax(T &a, const T &b) {
    if (b > a) {
        a = b;
        return true;
    }
    return false;
}

const int INFi = 2e9;
const ll INF = 1e18;
const int LG = 18;



struct dsu {
    vector<int> dsu;
    int n;

    int get_dsu(int a) {
        if (dsu[a] == a) return a;
        return dsu[a] = get_dsu(dsu[a]);
    }

    void build(int k) {
        n = k;
        dsu.resize(n);
        range(i, n) dsu[i] = i;
    }

    bool unio(int a, int b) {
        a = get_dsu(a), b = get_dsu(b);
        dsu[a] = b;
        return a == b;
    }
};

void solve() {
    int n, k;
    cin >> n >> k;
    vector<string> a(n);
    rep(i, n) cin >> a[i];
    vvi d(n, vi(n, -1));
    // x - y
    dsu D;
    D.build((n + 1) * (n + 1));
    rep(i, n) {
        rep(j, n) {
            if (a[i][j] == '*') {
                D.unio(i * (n + 1) + j, (i + 1) * (n + 1) + (j + 1));
            }
        }
    }
    queue<pi> q;
    auto Add = [&](int x, int y, int dist) {
        if (x < 0 || x >= n || y < 0 || y >= n || a[x][y] == '*' || d[x][y] != -1) return false;
        d[x][y] = dist;
        D.unio(x * (n + 1) + y, (x + 1) * (n + 1) + (y + 1));
        q.push({x, y});
        return true;
    };
    Add(0, 0, 0);
    vi dx = {0, 0, 1, -1};
    vi dy = {1, -1, 0, 0};
    while (!q.empty() && d[n - 1][n - 1] == -1) {
        auto [x, y] = q.front();
        q.pop();
        int dist2 = d[x][y] + 1;
        rep(w, 4) {
            int x2 = x + dx[w];
            int y2 = y + dy[w];
            Add(x2, y2, dist2);
        }
        int len = k / 2;
        while (true) {
            int p = D.get_dsu(x * (n + 1) + y);
            int x2 = p / (n + 1);
            int y2 = p % (n + 1);
            if (x2 == n || y2 == n || y2 - y > len) break;
            Add(x2, y2, dist2);
        }
        len = (k - 1) / 2;
        swap(x, y);
        x++;
        while (true) {
            int p = D.get_dsu(x * (n + 1) + y);
            int x2 = p / (n + 1);
            int y2 = p % (n + 1);
            if (x2 == n || y2 == n || y2 - y > len) break;
            Add(x2, y2, dist2);
        }
    }
    cout << d[n - 1][n - 1] << '\n';
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(12) << fixed;
    int t = 1;
    rep(i, t) {
        solve();
    }
    return 0;
}