#include <bits/stdc++.h>

using namespace std;

#define int long long
typedef long long ll;
const int P = 998244353;
typedef pair<ll,ll> PLL;
const int N = 5010;

const int mod = 1e9 + 7;

int n,m;
string Map[N];
bool Vis[N][N];
ll fx[4][2]={{1,0},{0,1},{-1,0},{0,-1}};


struct Point{
    ll x,y,step;
};


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

    cin>>n>>m;
    for(int i=1;i<=n;i++)
        cin>>Map[i],Map[i]=" "+Map[i];
    queue<Point> q;
    q.push({1,1,0});
    while(q.size())
    {
        auto T_T=q.front();
        q.pop();
        if(Vis[T_T.x][T_T.y])
            continue;
        if(T_T.x==n&&T_T.y==n)
        {
            cout<<T_T.step<<endl;
            return 0;
        }
        Vis[T_T.x][T_T.y]=true;
        for(int i=0;i<4;i++)
        {
            ll dx=T_T.x+fx[i][0];
            ll dy=T_T.y+fx[i][1];
            if(dx>=1&&dx<=n&&dy>=1&&dy<=n&&Map[dx][dy]!='*'&&!Vis[dx][dy])
                q.push({dx,dy,T_T.step+1});
        }
        ll k=m;
        PLL now={T_T.x,T_T.y};
        while(k--) {
            now = {now.second + 1, now.first};
            if (now.second <= n && Map[now.second][now.first] != '*' && !Vis[now.second][now.first])
                q.push({now.second, now.first, T_T.step + 1});
        }
    }

    cout<<"-1\n";

    return 0;
}