#include <bits/stdc++.h>
using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;

#define fi first
#define se second

template<typename T> inline T read() {
    T x = 0, f = 1; char ch = 0;
    for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
    for(; isdigit(ch); ch = getchar()) x = (x << 3) + (x << 1) + (ch - '0');
    return x * f;
}

template<typename T> inline void write(T x) {
    if(x < 0) putchar('-'), x = -x;
    if(x > 9) write(x / 10);
    putchar(x % 10 + '0');
}

template<typename T> inline void print(T x, char ed = '\n') {
    write(x), putchar(ed);
}

const int N = 5e3 + 10, dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1};

namespace GoedelMachine {
    struct node { int x, y, d; };
    queue<node> q;
    int n, k;
    bool vis[N][N], ban[N][N];

    void init() {}
    void main() {
        n = read<int>(), k = read<int>();
        for(int i = 1; i <= n; ++ i) {
            for(int j = 1; j <= n; ++ j) {
                char ch; cin >> ch;
                ban[i][j] = (ch == '*');
            }
        }
        q.push({1, 1, 0}), vis[1][1] = 1;
        while(q.size()) {
            node t = q.front(); q.pop();
            if(t.x == n && t.y == n) {
                print(t.d);
                return ;
            }
            for(int i = 0; i < 4; ++ i) {
                int nx = t.x + dx[i], ny = t.y + dy[i];
                if(nx < 1 || nx > n || ny < 1 || ny > n) continue;
                if(!vis[nx][ny] && !ban[nx][ny]) {
                    vis[nx][ny] = 1;
                    q.push({nx, ny, t.d + 1});
                }
            }
            int nx = t.x, ny = t.y;
            for(int i = 1; i <= k; ++ i) {
                int z = nx;
                nx = ny + 1, ny = z;
                if(nx > n || ny > n) break;
                if(!vis[nx][ny] && !ban[nx][ny]) {
                    vis[nx][ny] = 1;
                    q.push({nx, ny, t.d + 1});
                }
            }
        }
        print(-1);
    }
}

signed main() {
    int T = 1;
    //T = read<int>();
    while(T --) {
        GoedelMachine::init();
        GoedelMachine::main();
    }
    return 0;
}