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

#define DBG 0

int get_line(char *s, int max)
{
    int i;
    fgets(s,max,stdin);
    i = strlen(s) - 1;
    while (i >= 0 && s[i] == '\n')
        i--;
    i++;
    s[i] = 0;
    return i;
}

int sgetint(char **s, int *x)
{
    char *t = *s;
    
    while (isspace(*t)) t++;
    if (sscanf(t,"%d",x) != 1) return 0;
    while (*t && !isspace(*t)) t++;
    *s = t;
    return 1;
}
#define MAXS 10
#define MAXC 7
#define MAX 2000

int d[MAX][MAX];
char code[MAX][MAXC + 3];
int distance(int i, int j)
{
	int x, k;
	x = 0;
	for (k = 0; k < MAXC; k++) {
		if (code[i][k] != code[j][k])
			x++;
	}
	return x;
}

int main(void)
{
	int a, b, c;
	int i, j, k, N;
	int s, max;
	
	while (1) {
		scanf("%d\n",&N);
		if (N == 0) break;
		/*
		for (i = 0; i < N; i++) {
			for (j = 0; j < N; j++) {
				d[i][j] = -1;
			}
		}
		*/
		for (i = 0; i < N; i++) 
			d[i][i] = 0;
		for (i = 0; i < N; i++) {
			get_line(code[i],MAXC + 3);
			for (j = 0; j < i; j++) {
			d[i][j] = d[j][i] = distance(i,j);
			}
		}
#if DBG		
		for (i = 0; i < N; i++) {
			for (j = 0; j < N; j++) {
			 printf("%d %d = %d\n",i,j,d[i][j]);
			}
		}
#endif
		for (k = 0; k < N; k++) {
			for (i = 0; i < N; i++) {
				for (j = 0; j < N; j++) {
					a = d[i][k];
					b = d[k][j];
					c = d[i][j];
						a += b;
				   if (a < c)
					  d[i][j] = d[j][i] = a;
				}
			}
		}
		max = 2000000;
		for (i = 0; i < N; i++) {
			s = 0;
			for (j = 0; j < N; j++)
				s += d[i][j];
			if (s < max)
				max = s;
		}
	    printf("The highest possible quality is 1/%d.\n",max);
	}
    return 0;
}