#include<iostream>

#include<cstdio>

#include<algorithm>

#include<cstring>

#include<cmath>

#include<queue>

using namespace std;

typedef long long ll;

inline int read()

{

    int x=,f=; char ch=getchar();

    while(ch<''||ch>'') { if(ch=='-') f=-; ch=getchar(); }

    while(ch>=''&&ch<='') { x=(x<<)+(x<<)+(ch^); ch=getchar(); }

    return x*f;

}

const int N=1e6+,INF=1e9,xx[]={,,,,-,-,-,-},yy[]={,,-,-,-,-,,};

namespace Dinic {

    int fir[N],from[N<<],to[N<<],val[N<<],cntt=;

    int S,T,dep[N],Fir[N];

    queue <int> Q;

    inline void add(int a,int b,int c)

    {

        from[++cntt]=fir[a]; fir[a]=cntt;

        to[cntt]=b; val[cntt]=c;

        from[++cntt]=fir[b]; fir[b]=cntt;

        to[cntt]=a; val[cntt]=;

    }

    bool BFS()

    {

        for(int i=;i<=T;i++) Fir[i]=fir[i],dep[i]=;

        Q.push(S); dep[S]=;

        while(!Q.empty())

        {

            int x=Q.front(); Q.pop();

            for(int i=fir[x];i;i=from[i])

            {

                int &v=to[i]; if(dep[v]||!val[i]) continue;

                dep[v]=dep[x]+; Q.push(v);

            }

        }

        return dep[T]>;

    }

    int DFS(int x,int mxfl)

    {

        if(x==T||!mxfl) return mxfl;

        int fl=,res;

        for(int &i=Fir[x];i;i=from[i])

        {

            int &v=to[i]; if(dep[v]!=dep[x]+||!val[i]) continue;

            if( res=DFS(v,min(mxfl,val[i])) )

            {

                mxfl-=res; val[i]-=res;

                fl+=res; val[i^]+=res;

                if(!mxfl) break;

            }

        }

        return fl;

    }

    int dinic() { int res=; while(BFS()) res+=DFS(S,INF); return res; }

}

int n,a[][],id[][],tot;

char s[];

int main()

{

    n=read();

    for(int i=;i<=n;i++)

    {

        scanf("%s",s+); int len=strlen(s+);

        for(int j=;j<=len;j++)

        {

            a[i][j]=(s[j]=='');

            if(!a[i][j]) id[i][j]=++tot;

        }

    }

    Dinic::T=tot+;

    for(int i=;i<=n;i++)

        for(int j=;j<=n;j++)

        {

            if(a[i][j]) continue;

            if((i+j)&) { Dinic::add(id[i][j],Dinic::T,); continue; }

            Dinic::add(Dinic::S,id[i][j],);

            for(int k=;k<;k++)

            {

                int px=i+xx[k],py=j+yy[k];

                if(px<||px>n||py<||py>n||a[px][py]) continue;

                Dinic::add(id[i][j],id[px][py],INF);

            }

        }

    printf("%d\n",tot-Dinic::dinic());

    return ;

}