#include<cstdio>

#include<iostream>

#include<cstring>

#include<cstdlib>

#include<algorithm>

#include<cmath>

using namespace std;

const int dx[]={-,-,-,,,,,-};

const int dy[]={-,,,,,-,-,-};

struct node

{

    int x,y,c,next,other;

}a[];int len,last[];

void ins(int x,int y,int c)

{

    int k1,k2;

    len++;k1=len;

    a[len].x=x;a[len].y=y;a[len].c=c;

    a[len].next=last[x];last[x]=len;

    len++;k2=len;

    a[len].x=y;a[len].y=x;a[len].c=;

    a[len].next=last[y];last[y]=len;

    a[k1].other=k2;

    a[k2].other=k1;

}

int st,ed,h[],list[];

bool bt_h()

{

    memset(h,,sizeof(h));h[st]=;

    int head=,tail=;list[]=st;

    while(head!=tail)

    {

        int x=list[head];

        for(int k=last[x];k;k=a[k].next)

        {

            int y=a[k].y;

            if(a[k].c>&&h[y]==)

            {

                h[y]=h[x]+;

                list[tail]=y;

                tail++;

            }

        }

        head++;

    }

    if(h[ed]==)return false;

    return true;

}

int findflow(int x,int f)

{

    if(x==ed)return f;

    int s=;

    for(int k=last[x];k;k=a[k].next)

    {

        int y=a[k].y;

        if(a[k].c>&&h[y]==h[x]+&&s<f)

        {

            int t=findflow(y,min(a[k].c,f-s));

            s+=t;a[k].c-=t;a[a[k].other].c+=t;

        }

    }

    if(s==)h[x]=;

    return s;

}

int n,color[][];

char ss[];

bool mp[][];

int point(int x,int y){return (x-)*n+y;}

int main()

{

    scanf("%d",&n);

    int br;

    int sum=;

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

    {

        scanf("%s",ss+);

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

        {

            if(ss[j]=='')mp[i][j]=true, sum++;

            else           mp[i][j]=false;

        }

    }

    //-----sc-----

    memset(color,,sizeof(color));

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

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

            if(j==)color[i][j]=-color[i-][j];

            else     color[i][j]=-color[i][j-];

    //---paint_color---

    //----init-----

    st=n*n+,ed=n*n+;

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

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

            if(mp[i][j]==true)

            {

                if(color[i][j]==)

                    ins(st,point(i,j),);

                else

                    ins(point(i,j),ed,);

            }

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

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

            if(mp[i][j]==true&&color[i][j]==)

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

                {

                    int ti=i+dx[t],tj=j+dy[t];

                    if(ti>&&ti<=n&&tj>&&tj<=n&&mp[ti][tj]==true)

                        ins(point(i,j),point(ti,tj),);

                }

    //----composition------

    int ans=;

    while(bt_h()==true)

    {

        ans+=findflow(st,);

    }

    printf("%d\n",sum-ans);

    return ;

}