#include <vector>
#include <iostream>
#include <algorithm>
#include <string>

using namespace std;
int getn(string s) {
    int n = 0;
    string ans = "";
    for (int i = 0; i < s.size(); i++)
        if (isdigit(s[i]))
            ans.push_back(s[i]);
        else {
            if (n == 0)
                n += (stoi(ans) - 1) * 3600;
            else
                n += stoi(ans) * 60;
            ans = "";
        }

    n += stoi(ans);
    return n;
}

int main() {

    int n;
    cin >> n;
    vector <int> a(n);
    for (int i = 0; i < n; i++) {
        string s;
        cin >> s;
        a[i] = getn(s);
    }
    sort(a.begin(), a.end());
    vector <int> dp(43200, 0);
    int ind = 0;
    while (a[ind] == 0)
        ind++;
    for (int i = 0; i < n; i++) {
        if (a[i] != 0)
            dp[0] += 43200 - a[i];
    }
    //int r = dp[0];
    for (int i = 1; i < 43200; i++) {
        int r = dp[i - 1];
        int count = ind;
        while (ind < n && a[ind] == i)
            ind++;
        int d = dp[i - 1] + n - (ind - count) - 43200 * (ind - count);
        dp[i] = d;
    }

    int ans = 1e9;
    int t = 0;
    for (int i = 0; i < 43200; i++)
        if (dp[i] < ans) {
            ans = dp[i];
            t = i;
        }

    int h = t / 3600;
    int m = (t - h * 3600) / 60;
    int s = (t - h * 3600 - m * 60);

    string ss = "";
    h++;
    ss += to_string(h);
    ss += ":";
    if (m < 10) {
        ss += "0";
        ss += to_string(m);
    }
    else ss += to_string(m);
    ss += ":";
    if (s < 10) {
        ss += "0";
        ss += to_string(s);
    }
    else ss += to_string(s);
    cout << ss;

    return 0;
}