#include "bits/stdc++.h"

using namespace std;
using i64 = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, k;
    cin >> n >> k;
    vector<string> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    int sx = 0, sy = 0, tx = n - 1, ty = n - 1;
    queue<array<int, 3>> q;
    q.push({0, sx, sy});
    int dx[] = {+1, -1, +0, +0};
    int dy[] = {+0, +0, +1, -1};
    vector<vector<int>> vis(n, vector<int>(n));
    vis[sx][sy] = 1;
    while (!q.empty()) {
        auto [res, x, y] = q.front();
        if (x == tx && y == ty) {
            cout << res << '\n';
            return 0;
        } 
        q.pop();
        for (int i = 0; i < 4; i++) {
            int nx = x + dx[i];
            int ny = y + dy[i];
            if (nx < 0 || ny < 0 || nx >= n || ny >= n) {
                continue;
            }
            if (vis[nx][ny]) {
                continue;
            }
            if (a[nx][ny] == '*') {
                continue;
            }
            vis[nx][ny] = 1;
            q.push({res + 1, nx, ny});
        }

        int X = x, Y = y;
        for (int i = 0; i <= k; i++) {
            int nx = X;
            int ny = Y;
            if (nx < 0 || ny < 0 || nx >= n || ny >= n) {
                break;
            }
            if (vis[nx][ny]) {
                int tmp = X;
                X = Y + 1;
                Y = tmp;
                continue;
            }
            if (a[nx][ny] == '*') {
                int tmp = X;
                X = Y + 1;
                Y = tmp;
                continue;
            }
            vis[nx][ny] = 1;
            q.push({res + 1, nx, ny});
            int tmp = X;
            X = Y + 1;
            Y = tmp;
        }
    }
    cout << "-1\n";

    return 0;
}