#include <string>
#include <iostream>
#include <stdio.h>
#include <vector>
#include <set>
#include <map>
#include <algorithm>

using namespace std;

typedef long long LL;
typedef pair<int, int> pii;
typedef pair<LL, LL> pll;
typedef pair<string, string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
typedef vector<LL> vl;
typedef vector<vl> vvl;
#pragma warning(disable:4996)


struct t {
    long long hour, m, sec;
};

bool cmp(t a, t b) {
    if (a.hour != b.hour)
        return a.hour > b.hour;
    else if (a.m != b.m)
        return a.m > b.m;
    else
        return a.sec > b.sec;
}

int main() {
    int n;
    cin >> n;
    vector <long long> arr(n);

    for (int i = 0; i < n; i++) {
        long long x, y, z;
        scanf("%lld:%lld:%lld", &x, &y, &z);
        if (x == 12)
            arr[i] = y * 60 + z;
        else
            arr[i] = x * 3600 + y * 60 + z;
    }
    sort(arr.begin(), arr.end());
    vector <int> dp(n);
    for (int i = 1; i < n; i++) {
        dp[0] += 43200 - arr[i] + arr[0];
    }

    long long ans = arr[0];
    long long min = dp[0];
    for (int i = 1; i < n; i++) {
        dp[i] = dp[i - 1] - (43199 - arr[i] + arr[i - 1]) + (arr[i] - arr[i - 1]) * (n - 1);
        if (dp[i] < min)
            ans = arr[i], min = dp[i];
    }

    long long ans_hour, ans_min, ans_sec;
    ans_sec = ans % 3600 % 60;
    ans_hour = ans / 3600;

    if (ans_hour == 0)
        ans_hour = 12;
    ans_min = ans % 3600 / 60;
    printf("%lld:%02lld:%02lld", ans_hour, ans_min, ans_sec);
    return 0;
}