#include <stdio.h>
#define NMax 1005 //!!!!!!!!!!!

int n;
int p[NMax][NMax];
char s[NMax][NMax];


int main()
{
  int i, j, k, max, val, min;
  //freopen("C.in", "rt", stdin);

  scanf("%d\n", &n);

  while (n)
  {
    for (i = 0; i < n; i++)
      scanf("%s\n", s[i]);

    for (i = 0; i < n; i++)
    {
      for (j = 0; j < n; j++)
      {
        for (k = 0; i - k >= 0 && j + k < n && s[i - k][j] == s[i][j + k]; k++);
        p[i][j] = k;
      }
    }


    max = -1;
    for (i = 0; i < n; i++)
    {
      for (j = 0; j < n; j++)
      {

        val = p[i][j];

        if (p[i][j] > max)
        {
          for (k = 0; k <= p[i][j] && val > max; k++)
          {
            if (val > p[i-k][j+k] + k)
              val = p[i-k][j+k] + k;

            min = val;
            if (min > k + 1)
              min = k + 1;

            if (max < min)
              max = min;
          }
        }
      }
    }

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


    scanf("%d\n", &n);
  }


  return 0;
}