#include<iostream>

 #include<algorithm>

 #include<cstring>

 using namespace std;

 const int INF = ;

 int x, y;

 int d[][];

 void Floyd()

 {

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

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

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

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

 }

 int main()

 {

     //freopen("D:\\txt.txt", "r", stdin);

     int kase = ;

     while (cin >> x >> y && (x!= || y!=))

     {

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

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

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

         else d[i][j] = INF;

         do

         {

             d[x][y] = ;

         } while (cin >> x >> y && (x!= || y!=));

         Floyd();

         double ans = ;

         int count = ;

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

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

         {

             if (i!=j && d[i][j] < INF)

             {

                 count++;

                 ans += d[i][j];

             }

         }

         printf("Case %d: average length between pages = %.3f clicks\n", ++kase, ans / count);

     }

 }