#include <bits/stdc++.h>
using namespace std;

#define int long long
const int M = 1e9+7;
const int N = 1e7+5;
const int INF = LLONG_MAX;
int n, m;
vector<vector<int>> adj;
int memo[105][105][105];
int floyd(int i, int j, int k) {
    if(k == 0) return adj[i][j];
    if(memo[i][j][k] != LLONG_MIN) return memo[i][j][k];
    __int128 a = floyd(i, k, k-1);
    __int128 b = floyd(k, j, k-1);
    int via = (a >= INF || b >= INF) ? INF : a + b;
    int res = min(floyd(i, j, k-1), via);

    // int res = min(floyd(i, j, k-1), floyd(i, k, k-1) + floyd(k, j, k-1));
    return memo[i][j][k] = res;
}
int32_t main() {
    cout << fixed << setprecision(3);
    int tt = 1;
    int a, b;
    while((cin >> a >> b) && (a != 0 && b != 0)) {
        vector<pair<int, int>> edges;
        edges.push_back({a, b});
    int u, v;
    int maxi = max(a, b);
    while((cin >> u >> v) && (u != 0 && v != 0)) {
        edges.push_back({u, v});
        maxi = max({u,v,maxi});
    }
    n = maxi;
    m = edges.size();
    // cin >> n >> m;
    adj.assign(n+1, vector<int>(n+1, INF));
    for (auto [u,v] : edges)
    {
        // int u, v;
        // cin >> u >> v;
        adj[u][v] = 1;
    }
    for (int i = 1; i < 105; ++i)
    {
        for (int j = 1; j < 105; ++j)
        {
            for(int k=1;k<105;++k) {
                memo[i][j][k] = LLONG_MIN;
            }
        }
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= n; ++j)
        {
            if(i == j) adj[i][j] = 0;
            // else if(adj[i][j] == 0) adj[i][j] = INF;
        }
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= n; ++j)
        {
            floyd(i, j, n);
        }
    }
    int sum = 0, cnt = 0;
    for(int i=1;i<=n;++i) {
        for(int j=1;j<=n;++j) {
            if(memo[i][j][n]!= INF && i != j){
                sum+=(memo[i][j][n]);
                cnt++;
            }
            // cout << memo[i][j][n] << " ";
        }
        // cout << endl;
    }
    if(tt != 1) cout << endl;
    cout << "Case " << tt++
    << ": average length between pages = "
    <<((double)sum / cnt) << " clicks";
    }
    return 0;
}