#include <stdio.h>
#include <stdlib.h>

#define DEBUG 0
#define MAXT 2048
#define TNAMELEN 16
#define TRL 7

char trucks[MAXT][TNAMELEN];
int N, edgeno;
unsigned int edges[MAXT*MAXT];


#define FROM(i) (i&0x07ff)
#define TO(i) ((i>>12)&0x07ff)
#define WEIGHT(i) (i>>24)
#define CONSTRUCT(f, t, w) (((w&0xff) << 24) | (t << 12) | f)

struct {
  unsigned father;
  int size;
} uftrucks[MAXT];

int
uffind(int a)
{
  int b = a, c;
  while (uftrucks[b].father != b)
    b = uftrucks[b].father;
  while (uftrucks[a].father != a)
    {
      c = uftrucks[a].father;
      uftrucks[a].father = b;
      a = c;
    }
  return b;
}

int
ufunion (int a, int b)
{
  a = uffind(a);
  b = uffind(b);
  if (uftrucks[a].size > uftrucks[b].size) {
    uftrucks[b].father = a;
    uftrucks[a].size += uftrucks[b].size;
  } else {
    uftrucks[a].father = b;
    uftrucks[b].size += uftrucks[a].size;
  }
  return uftrucks[a].father;
}

void
ufinit(int s)
{
  int i;
  for (i = 0; i < s; i++)
    {
      uftrucks[i].size = 1;
      uftrucks[i].father = i;
    }
}

int
cmp(const void *a, const void *b)
{
  unsigned int ax = *(unsigned int const *) a;
  unsigned int bx = *(unsigned int const *) b;

  return (int)WEIGHT(ax) - (int)WEIGHT(bx);
}

int
main(void)
{
  int i, j, k;
  int diffs, ksize, sum;

  for (;;)
    {
      scanf("%d ", &N);
      if (!N)
	break;
      edgeno = 0;
      for (i = 0; i < N; i++)
	fgets(trucks[i], TNAMELEN, stdin);
      for (i = 0; i < N; i++)
	for (j = i+1; j < N; j++)
	  {
	    diffs = 0;
	    for (k = 0; k < TRL; k++)
	      if (trucks[i][k] != trucks[j][k])
		diffs++;
	    edges[edgeno++] = CONSTRUCT(i, j, diffs);
	  }
      qsort(edges, edgeno, sizeof(*edges), cmp);
      ksize = 0; sum = 0;
      ufinit(N);
      for (i = 0; ksize < N-1; i++) {
#if DEBUG
	printf("From: %d, To: %d, Weight: %d, I: %d, Ksize: %d, UFF: %d, UFT %d ", FROM(edges[i]), TO(edges[i]), WEIGHT(edges[i]), i, ksize, uffind(FROM(edges[i])), uffind(TO(edges[i])));
#endif
	if (uffind(FROM(edges[i])) != uffind(TO(edges[i]))) {
	  ufunion(FROM(edges[i]), TO(edges[i]));
	  ksize++;
	  sum += WEIGHT(edges[i]);
#if DEBUG
	  printf("Added\n");
#endif
	} else {
#if DEBUG
	  printf("\n");
#endif  
	}
      }
      printf ("The highest possible quality is 1/%d.\n", sum);
    }
  return EXIT_SUCCESS;
}