#include<cstdio>

 #include<cstring>

 #include<algorithm>

 using namespace std;

 const int N=1e3+;

 char map[N][N];

 int dp[N][N];

 int main(){

     int n;

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

         memset(dp,,sizeof(dp));

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

             getchar();

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

                 scanf("%c",&map[i][j]);

             }

         }

         int ans=;

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

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

                 if(i==||j==n){

                     dp[i][j]=;

                     continue;

                 }

                 int t1=i,t2=j,cnt=;

                 while(t1>=&&t2<=n&&map[t1][j]==map[i][t2]){

                     t1--;

                     t2++;

                     cnt++;

                 }

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

                     dp[i][j]=dp[i-][j+]+;

                 else

                     dp[i][j]=cnt;

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

             }

         }

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

     }

 }