#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

using namespace std;

typedef long long ll;
#define all(x) begin(x), end(x)
constexpr int INF = (1 << 30) - 1;
constexpr long long IINF = (1LL << 60) - 1;
constexpr int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

template <class T> istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) is >> x;
    return is;
}

template <class T> ostream& operator<<(ostream& os, const vector<T>& v) {
    auto sep = "";
    for (const auto& x : v) os << exchange(sep, " ") << x;
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = forward<U>(y), true); }

template <class T> void mkuni(vector<T>& v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <class T> int lwb(const vector<T>& v, const T& x) { return lower_bound(begin(v), end(v), x) - begin(v); }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, k;
    cin >> n >> k;
    vector<string> S(n);
    for (auto& s : S) cin >> s;

    vector dp(n, vector<pair<int, int>>(n, {INF, INF}));
    vector<queue<pair<int, int>>> cur(k + 1), nxt(k + 1);
    dp[0][0] = {0, k};
    cur[k].emplace(0, 0);
    auto calc = [&](int x, int y) -> pair<int, int> { return {y + 1, x}; };
    for (int d = 0, update = 0;; d++) {
        for (int e = 1; e <= k; e++) {
            while (not cur[e].empty()) {
                auto [x, y] = cur[e].front();
                cur[e].pop();
                if (dp[x][y] != make_pair(d, e)) continue;
                for (int i = 0; i < 4; i++) {
                    int nx = x + dx[i], ny = y + dy[i];
                    if (min(nx, ny) < 0 or n <= max(nx, ny)) continue;
                    if (S[nx][ny] == '*') continue;
                    if (make_pair(d + 1, k) < dp[nx][ny]) {
                        dp[nx][ny] = {d + 1, k};
                        nxt[k].emplace(nx, ny);
                        update = 1;
                    }
                }
                {
                    int cnt = 0;
                    while (true) {
                        auto [nx, ny] = calc(x, y);
                        x = nx, y = ny;
                        cnt++;
                        if (n <= max(x, y)) {
                            cnt = INF;
                            break;
                        }
                        if (S[x][y] == '.') break;
                    }
                    if (cnt > k) continue;
                    int nd = d, ne = e;
                    if (ne + cnt <= k)
                        ne += cnt;
                    else {
                        nd++;
                        ne = cnt;
                    }
                    if (make_pair(nd, ne) < dp[x][y]) {
                        dp[x][y] = {nd, ne};
                        if (nd == d)
                            cur[ne].emplace(x, y);
                        else {
                            nxt[ne].emplace(x, y);
                            update = 1;
                        }
                    }
                }
            }
        }
        swap(cur, nxt);
        if (not exchange(update, 0)) break;
    }

    int ans = dp[n - 1][n - 1].first;
    cout << (ans == INF ? -1 : ans) << '\n';
    return 0;
}