#include <stdio.h>
#include <string.h>
#define N 2002

int n;//number of truck 2..2000
char truck[N][7];//different types of truck
int M[N][N];//distance between 2 trucks
int lowcost[N];//辅助数组
int visited[N];//记录是否被放进最小生成树中
int dis(int i,int j)//计算i,j类truck的不同
{
    int k,c=0;
    for (k=0;k<7;k++)
        if(truck[i][k]!=truck[j][k])
            c++;
    return c;
}
int min_lowcost(int *m)
{
    int i,t;
    for (i=0;i<n;i++)
        if (!visited[i]&&lowcost[i]<(*m))
        {
            t=i;
            (*m)=lowcost[i];
        }            
    return t;
}
int Prim()
{
    int i,mindis=0,next_idx,j,next_len;

    for (i=0;i<n;i++)
    {
        visited[i]=0;
        lowcost[i]=M[0][i];//和衍生图中距离最近的那个点的距离
    }
    visited[0]=1;
    for (i=1;i<n;i++)//将其余n-1辆车放入衍生图
    {
        next_len=8;
        next_idx=min_lowcost(&next_len);//找出花费最小的车next
        mindis+=next_len;//最小生成树累加
        visited[next_idx]=1;//添加到衍生图
        for (j=0;j<n;j++)//更新辅助数组
        {
            if(!visited[j]&&M[next_idx][j]<lowcost[j])
                lowcost[j]=M[next_idx][j];
        }
    }
    return mindis;
}
int main()
{
    int i,j;
    while(scanf("%d",&n)!=EOF)
    {
        if (n==0)    break;
        //read info
        memset(truck,0,sizeof(truck));
        for (i=0;i<n;i++)
            scanf("%s",truck[i]);
        //init Metric
        memset(M,8,sizeof(M));
        for (i=0;i<n;i++)
            for (j=i+1;j<n;j++)
                M[i][j]=M[j][i]=dis(i,j);
        //output result
        printf("The highest possible quality is 1/%d.\n",Prim());
    }
    return 1;
}