821

#include <iostream>
#include <string.h>
#include <stdio.h>
#include <map>

#define INF 1000000000

using namespace std;

map<int,int> m;
int graph[105][105];
int sum[105];
double total;

int main()
{
	int a,b,cnt;
	int kase =1;
	while(cin>>a)
	{
		cin>>b;
		if(a==0 && b==0)
		break;

		for(int i=1;i<101;i++)
		{
			sum[i]=0;
			for(int j=1;j<101;j++)
			{
				graph[i][j]=INF;
				if(i==j)
				graph[i][j]=0;
			}
		}
		cnt=1;
		m.clear();

		m[a]=cnt;
		if(m[b]==0)
		{
			cnt+=1;
			m[b]=cnt;
		}

		graph[m[a]][m[b]]=1;

		while(cin>>a)
		{
			cin>>b;
			if(a==0 && b==0)
			break;

			if(m[a]==0)
			{
				cnt+=1;
				m[a]=cnt;
			}
			if(m[b]==0)
			{
				cnt+=1;
				m[b]=cnt;
			}

			graph[m[a]][m[b]]=1;
		}

		int len = m.size();
		for(int k=1;k<=len;k++)
		{
			for(int i=1;i<=len;i++)
			{
				for(int j=1;j<=len;j++)
				{
					if(graph[i][j]>(graph[i][k]+graph[k][j]))
						graph[i][j] = (graph[i][k]+graph[k][j]);
				}
			}
		}

		total = 0;
		for(int i=1;i<=len;i++)
		{
			for(int j=1;j<=len;j++)
			{
				sum[i]+=graph[i][j];
			}
			total+=sum[i];
		}

		//cout<<"t = "<<total<<"\n";
		//cout<<"len ="<<len*(len-1)<<"\n";
		total/=(len*(len-1));

		cout<<"Case "<<kase++<<": average length between pages = ";
		printf("%.3lf",total);
		cout<<" clicks\n";
	}

	return 0;
}