TV

#include <fstream>
using namespace std;

ifstream fin("tv.in");ofstream fout("tv.out");
//ifstream fin("input");ofstream fout("output");

int k, n, maxx = 0, ans1, ans2;
int dur, h, m, s;
int mars[100005];
int hs = 3600 * 24;

void afis(int nr) {
    h = nr / 3600; nr -= h * 3600;
    m = nr / 60; nr -= m * 60;
    s = nr;
    if (h < 10) {
        fout << 0;
    }
    fout << h << ":";
    if (m < 10) {
        fout << 0;
    }
    fout << m << ":";
    if (s < 10) {
        fout << 0;
    }
    fout << s;
}

int main() {
    fin >> k;
    fin >> n;
    for (int i = 1; i <= n; i++) {
        char c;
        fin >> dur >> h >> c >> m >> c >> s;
        mars[s + 60 * m + 3600 * h] += 1;
        mars[s + 60 * m + 3600 * h + dur] -= 1;
    }
    ans1 = hs;
    for (int i = 0; i < hs; i++) {
        mars[i] = mars[i - 1] + mars[i];
        if (mars[i] > maxx) {
            maxx = mars[i];
            ans2 = i;
        }
        if (mars[i]) {
            ans1--;
        }

    }

    if (k == 1) {
        afis(ans1);
    }
    else {
        afis(ans2);
    }
}