#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include <cmath>

 #include<stack>

 #include<vector>

 #include<map>

 #include<set>

 #include<queue>

 #include<algorithm>

 using namespace std;

 typedef long long LL;

 const int INF = (<<)-;

 const int mod=;

 const int maxn=;

 int d[maxn][maxn];

 int main(){

     int n,m,u,v,ans,kase=;

     while(scanf("%d %d",&u,&v)!=EOF){

         memset(d,,sizeof(d));

         if(u==&&v==) break;        

          for(int i=;i<=;i++){

             for(int j=;j<=;j++){

                 if(i==j) d[i][j]=;

                 else d[i][j]=INF;

             }

         }

         n=max(u,v);d[u][v]=;

         while(scanf("%d %d",&u,&v)!=EOF){

             if(u==&&v==) break;

             n=max(max(u,v),n);

             d[u][v]=;

         }

         for(int k=;k<=n;k++)

          for(int i=;i<=n;i++)

           for(int j=;j<=n;j++)

           if(d[i][k]<INF&&d[k][j]<INF)

            d[i][j]=min(d[i][j],d[i][k]+d[k][j]);

            int sum=,cnt=;

            for(int i=;i<=n;i++)

             for(int j=;j<=n;j++)

                 if(d[i][j]!=INF&&d[i][j]!=) sum+=d[i][j],cnt++;

             double tmp=1.0*sum/cnt;

              printf("Case %d: average length between pages = %.3lf clicks\n",++kase,tmp);

     }

     return ;

 }