#include<iostream>
#include<cmath>
#include<cstring>
#include<queue>
#include<vector>
#include<cstdio>
#include<algorithm>
#include<map>
#include<set>
#define rep(i,e) for(int i=0;i<(e);i++)
#define rep1(i,e) for(int i=1;i<=(e);i++)
#define repx(i,x,e) for(int i=(x);i<=(e);i++)
#define X first
#define Y second
#define PB push_back
#define MP make_pair
#define mset(var,val) memset(var,val,sizeof(var))
#define scd(a) scanf("%d",&a)
#define scdd(a,b) scanf("%d%d",&a,&b)
#define scddd(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define pd(a) printf("%d\n",a)
#define scl(a) scanf("%lld",&a)
#define scll(a,b) scanf("%lld%lld",&a,&b)
#define sclll(a,b,c) scanf("%lld%lld%lld",&a,&b,&c)
#define IOS ios::sync_with_stdio(false);cin.tie(0)using namespace std;
typedef long long ll;
template <class T>
void test(T a){cout<<a<<endl;}
template <class T,class T2>
void test(T a,T2 b){cout<<a<<" "<<b<<endl;}
template <class T,class T2,class T3>
void test(T a,T2 b,T3 c){cout<<a<<" "<<b<<" "<<c<<endl;}
template <class T>
inline bool scan_d(T &ret){char c;int sgn;if(c=getchar(),c==EOF) return 0;while(c!='-'&&(c<'0'||c>'9')) c=getchar();sgn=(c=='-')?-1:1;ret=(c=='-')?0:(c-'0');while(c=getchar(),c>='0'&&c<='9') ret = ret*10+(c-'0');ret*=sgn;return 1;
}
//const int N = 1e6+10;
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3fll;
const ll mod = 1000000000;
int T;void testcase(){printf("Case %d:",++T);
}const int MAXN = 2500 ;
const int MAXM = 250;
const double eps = 1e-8;
const double PI = acos(-1.0);bool vis[MAXN];
int lowc[MAXN];
int cost[MAXN][MAXN];int Prim(int n){int ans=0;mset(vis,false);vis[0]=true;for(int i=1;i<n;i++) lowc[i]=cost[0][i];for(int i=1;i<n;i++){int minc = inf;int p = -1;for(int j=0;j<n;j++){if(!vis[j]&&minc>lowc[j]){minc = lowc[j];p = j;}}if(minc == inf){return -1;}ans+=minc;vis[p]=true;for(int j=0;j<n;j++){if(!vis[j]&&lowc[j]>cost[p][j]){lowc[j] = cost[p][j];}}}return ans;
}
char s[MAXN][10];
int main() {
#ifdef LOCALfreopen("in.txt","r",stdin);
#endif // LOCALint n;while(~scanf("%d",&n)&&n){for(int i=0;i<n;i++){scanf("%s",s[i]);for(int j=0;j<i;j++){int cnt=0;for(int k=0;k<7;k++){cnt += s[i][k]==s[j][k];}cost[i][j]=cost[j][i]=7-cnt;}}int ans=Prim(n);printf("The highest possible quality is 1/%d.\n",ans);}return 0;
}