#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

#define forn(i, n) for(int i = 0; i < (int) (n); i++)
const double eps = 1e-4;

int main(){
#ifdef ACM
    freopen("test.in", "r", stdin);
#endif

    double s[16], e[16]; int n;
    int counter = 1;

    while(scanf("%d", &n) && n != 0){
        forn(i, n){
            scanf("%lf %lf", &s[i], &e[i]);
        }

        double l = 0, r = 1440*60;
        while(r-l > eps){
            double m = (l + r)/2;

            vector<int> perm;
            forn(i, n) perm.push_back(i);

            bool ok = false;
            do{
                double d = s[ perm[0] ];
                bool allset = true;

                forn(i, n){
                    if(d <= e[ perm[i] ]){
                        d = max(s[ perm[i] ], d)+m;
                    }else{
                        allset = false;
                        break;
                    }
                }

                if(allset){ ok = true; break; }
            }while(next_permutation(perm.begin(), perm.end()));

            if(ok) l = m; else r = m;
        }

        int hours = (int) l;
        int mins = round((l - hours)*60.0);
        if(mins == 60) hours++, mins = 0;

        printf("Case %d: %d:%02d\n", counter++, hours, mins);
    }


    return 0;
}