#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>using namespace std;
char mp[510][510];
int vis[510][510];
int are_num[250050];
int sum[510][510];
int are_vis[250050];
int cnt=0,tmp=0;
int ans=0,ans_temp=0,k;
void dfs(int i,int j)
{
//    printf ("%d %d\n",i,j);if (mp[i][j]=='X'||vis[i][j]) return ;vis[i][j]=cnt;tmp++;dfs(i+1,j);dfs(i-1,j);dfs(i,j+1);dfs(i,j-1);
}
void add(int i,int j)
{if (!vis[i][j])return ;int t=vis[i][j];if (!are_vis[t]) ans_temp+=are_num[t];are_vis[t]++;
}
void pop(int i,int j)
{if (!vis[i][j])return ;int t=vis[i][j];are_vis[t]--;if (!are_vis[t]) ans_temp-=are_num[t];
}
int clac(int x,int y){return sum[x+k-1][y+k-1]-sum[x+k-1][y-1]-sum[x-1][y+k-1]+sum[x-1][y-1];
}
int main()
{int n;scanf ("%d%d",&n,&k);memset(mp,'X',sizeof(mp));for (int i=1;i<=n;i++){scanf ("%s",mp[i]+1),mp[i][n+1]='X';}for (int i=1;i<=n;i++){for (int j=1;j<=n;j++){if (!vis[i][j]&&mp[i][j]=='.'){++cnt;tmp=0;dfs(i,j);are_num[cnt]=tmp;}}}for (int i=1;i<=n;i++){for (int j=1;j<=n;j++){sum[i][j]=sum[i-1][j]+sum[i][j-1]-sum[i-1][j-1];if (mp[i][j]=='.') sum[i][j]++;
//            printf ("%d ",sum[i][j]);
        }
//        printf ("\n");
    }for (int i=1;i<=n-k+1;i++){ans_temp=0;memset(are_vis,0,sizeof(are_vis));for (int x=i-1;x<=i+k;x++){for (int y=1;y<=k;y++){add(x,y);
//                printf ("加(%d %d)\n",x,y);
//                printf ("ans_temp==%d\n",ans_temp);
            }}for (int x=i;x<=i+k-1;x++)add(x,k+1);
//            printf ("加(%d %d)\n",x,k+1);
//        system("pause");
//printf ("%d\n",ans_temp);ans=max(ans,ans_temp+k*k-clac(i,1));
//        cout<<"start"<<ans_temp+k*k-(sum[k+i-1][k]-sum[i-1][k])<<endl;
//        cout<<"zhong"<<sum[k+i-1][k]<<'-'<<sum[i-1][k]<<endl;for (int j=2;j+k-1<=n;j++){for (int x=i;x<=i+k-1;x++)pop(x,j-2),add(x,j+k);
//                printf ("-(%d,%d)\n",x,j-2),printf ("+(%d,%d)\n",x,j+k);pop(i-1,j-1);pop(i+k,j-1);
//            printf ("-(%d,%d)\n",i-1,j-1);
//            printf ("-(%d,%d)\n",i+k,j-1);add(i-1,j+k-1);add(i+k,j+k-1);
//            printf ("+(%d,%d)\n",i-1,j+k-1);
//            printf ("+(%d,%d)\n",i+k,j+k-1);
//            printf ("%d\n",ans_temp);
//            system("pause");
//            cout<<"go"<<ans_temp+k*k-(sum[i+k-1][j+k-1]-sum[i+k-1][j-1]-sum[i-1][j+k-1]+sum[i-1][j-1])<<endl;ans=max(ans,ans_temp+k*k-clac(i,j));}}printf ("%d\n",ans);
//    for (int i=0;i<=n+1;i++)
//    {
//        for (int j=0;j<=n+1;j++)
//        {
//            printf ("%d",vis[i][j]);
//        }
//        printf ("\n");
//    }
//    for (int i=1;i<=cnt;i++) printf ("%d ",are_num[i]);return 0;
}