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

using namespace std;

int main() {
    int n;
    freopen("input.txt", "r", stdin);
    scanf("%d", &n);
    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        int h, m, s;
        scanf("%d:%d:%d", &h, &m, &s);
        a[i] = h * 3600 + m * 60 + s - 3600;
    }
    sort(a.begin(), a.end());
    long long sum = 0, mi, time;
    for (int i = 0;i < n - 1; ++i) {
        sum += a.back() - a[i];
    }
    mi = sum;
    time = a.back();
    int last = 1;
    for (int i = n - 2; i >= 0; --i) {
        sum -= (i + 1) * (a[i + 1] - a[i]);
        if (a[i] != a[i + 1]) {
            sum -= (n - i - 2) * (a[i + 1] - a[i]) * last;
            sum += (3600 * 12 - a[i + 1] + a[i]) * last;
            last = 1;
        } else {
            last++;
        }
        if (mi > sum) {
            mi = sum;
            time = a[i];
        }
    }
    time += 3600;
    printf("%d:", time / 3600);
    time %= 3600;
    printf("%02d:", time / 60);
    time %= 60;
    printf("%02d", time);
    return 0;
}