#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<cmath>

#include<algorithm>

#include<cstring>

#include<cstring>

#include<vector>

#include<queue>

#include<stack>

using namespace std;

char s[][];

int dp[][];

int main()

{

    int n;

    while(~scanf("%d",&n),n)

    {

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

         scanf("%s",s[i]+);

        memset(dp,,sizeof(dp));

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

         dp[i][]=;

        int ans=;

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

        {

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

           {

               dp[i][j]=;

               int l=min(j-,n-i);

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

               {

                  int x=i+k;

                  int y=j-k;

                  if(s[i][y]!=s[x][j])

                    break;

                  if(dp[i+][j-]>=k)dp[i][j]=k+;

               }

               ans=max(ans,dp[i][j]);

           }

        }

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

    }

    return ;

}