#include <cstdio>
    #include <algorithm>
    #include <cstring>
    #include <iostream>
 
    using namespace std;
 
    #define INF 1e9
    #define MAX_SIZE 100
 
	int graph[MAX_SIZE + 1][MAX_SIZE + 1], n, mapping[MAX_SIZE + 1];
	int main() {
		int u, v, flag=0, testCase = 1;
    	while(scanf("%d%d", &u, &v), u||v){
            for(int i = 1; i <= MAX_SIZE; i++) {
            	for(int j = 1; j <= MAX_SIZE; j++) {
                	graph[i][j] = INF;
            	}
            	graph[i][i] = 0;
            }
            int n = 0;
            memset (mapping, 0, sizeof(mapping));
            do {
            	if (!mapping[u])
            		mapping[u] = ++n;
            	if (!mapping[v])
            		mapping[v] = ++n;
            	graph[mapping[u]][mapping[v]] = 1;
            } while(scanf("%d%d", &u, &v), u||v);
 
            for(int k = 1; k <= n; k++)
	            for(int i = 1; i <= n; i++)
    		        for(int j = 1; j <= n; j++)
            		    graph[i][j] = min(graph[i][j], graph[i][k] + graph[k][j]);
 
        	double s = 0.0;
            for(int i = 1; i <= n; i++)
            	for(int j = 1; j <= n; j++)
            		s += graph[i][j];
            //cout<<s<<endl;
            s /= (double)n*(n-1);
            //cout<<s<<endl;
            printf("Case %d: average length between pages = %.3lf clicks\n",testCase++,s);
        }
        return 0;
    }

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