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

template<class T>
bool chmax(T& a, const T& b) {
    if (a < b) { a = b; return true; }
    return false;
}
template<class T>
bool chmin(T& a, const T& b) {
    if (b < a) { a = b; return true; }
    return false;
}

// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

// std::vector Declaration and Initialization
template<typename T>
vector<T> make_vector(size_t a, T x) { return vector<T>(a, x); }
template<typename T, typename U, typename... Ts>
auto make_vector(size_t a, U b, Ts... ts) {
    return vector<decltype(make_vector<T>(b,ts...))>(a, make_vector<T>(b, ts...));
}

// std::vector Input
template<typename T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto &e : v) is >> e;
    return is;
}

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::array Debug
template<typename T, size_t n>
ostream& operator<<(ostream& os, const array<T, n>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::deque Debug
template<typename T>
ostream& operator<<(ostream& os, const deque<T>& d) {
    os << "[";
    bool a = 1;
    for (auto e : d) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << " " << p.second << ")";
    return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
    os << "{";
    bool a = 1;
    for (auto e : mp) {
        os << (a ? "" : " ");
        os << e.first << ":" << e.second;
        a = 0;
    }
    os << "}";
    return os;
}

// std::tuple Debug
template<int N, class Tuple>
void out(ostream& os, const Tuple& t){}
template<int N, class Tuple, class H, class ...Ts>
void out(ostream& os, const Tuple& t) {
    if (N) os << " ";
    os << get<N>(t);
    out<N+1,Tuple,Ts...>(os, t);
}
template<class ...Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
    os << "(";
    out<0,tuple<Ts...>,Ts...>(os, t);
    os << ")";
    return os;
}

// Debug
#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl

// Weighted edge
template<typename T>
struct edge {
    int src, to;
    T cost;

    edge() {}
    edge(int to, T cost) : src(-1), to(to), cost(cost) {}
    edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

    friend ostream& operator<<(ostream& os, const edge& e) {
        return os << "(" << e.src << "->" << e.to << ":" << e.cost << ")";
    }
};

using LL = int64_t;

#define fs first
#define sc second

const int64_t MOD = 1e9+7;

struct Time {
    int h, m, s;
    friend ostream& operator<<(ostream& os, const Time& time) {
        return os << time.h << ":" << time.m << ":" << time.s;
    }
};

int calc(const Time& time) {
    return time.h * 60 * 60 + time.m * 60 + time.s;
}
void push_time(vector<pair<Time,int>>& time, int s, int t, int u, int i) {
    if (t / 12 != s % 5) {
        return;
    }
    time.emplace_back(Time{s / 5, t, u}, i);
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    while (true) {
        int n; cin >> n;
        if (n == 0) break;
        vector<pair<Time, int>> time;
        for (int i = 0; i < n; ++i) {
            int s, t, u; cin >> s >> t >> u;
            for (int k = 0; k < 60; ++k) {
                int S = (s + k) % 60,
                    T = (t + k) % 60,
                    U = (u + k) % 60;
                push_time(time, S, T, U, i);
                push_time(time, S, U, T, i);
                push_time(time, T, S, U, i);
                push_time(time, T, U, S, i);
                push_time(time, U, S, T, i);
                push_time(time, U, T, S, i);
            }
        }

        vector<pair<int,int>> ord;
        for (int i = 0; i < time.size(); ++i) {
            ord.emplace_back(calc(time[i].first), i);
        }

        sort(ord.begin(), ord.end());


        int l = 0, r = 0;
        vector<int> cnt(n);
        auto check = [&]() {
            for (int i = 0; i < n; ++i) {
                if (cnt[i] == 0) return false;
            }
            return true;
        };

        int ans = numeric_limits<int>::max();
        Time start, end;
        while (l < ord.size()) {
            assert(l <= r);
            while (r < ord.size() and !check()) {
                ++cnt[time[ord[r].second].second];
                ++r;
            }
            if (!check()) {
                break;
            }
            // [l, r) satisfies the condition.
            if (l < r and chmin(ans, ord[r-1].first - ord[l].first)) {
                start = time[ord[l].second].first;
                end = time[ord[r-1].second].first;
            }
            --cnt[time[ord[l].second].second];
            ++l;
        }
        printf("%02d:%02d:%02d %02d:%02d:%02d\n",
                start.h, start.m, start.s,
                end.h, end.m, end.s);
    }

    return 0;
}



Measured memory_bytes: 3280