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#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
//#include <chrono>
//#include <fstream>
//#include <bits/stdc++.h>
#include <math.h>

#define mp make_pair
#define pb push_back
#define eb emplace_back
#define x first
#define y second
#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,b,a) for (int i = (b) - 1; i >= (a); i--)

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<int> veci;
typedef vector<bool> vecb;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;

int v, d, n;
vector<pi> vec;
int max_len;

int str_to_int(string str) {
    return ((str[0] - '0') * 10 + str[1] - '0') * 60 + ((str[3] - '0') * 10 + str[4] - '0');
}

string int_to_str(int time) {
    return string(to_string(((time / 60) / 10)) + to_string(((time / 60) % 10)) + ':' + to_string(((time - (time / 60) * 60) / 10)) + to_string(((time - (time / 60) * 60) % 10)));
}

bool check(double cur) {
    int cnt = 0;
    vector<bool> used(n);
    for (int i = 0; i < n; i++)
        if ((cnt) * d + cur + (double)vec[i].x / v >= vec[i].y) {
            cnt++;
            used[i] = 1;
        }
    for (int i = n - 1; i >= 0; i--)
        if (!used[i] && (cnt) * d + cur + (double)(2 * max_len - vec[i].x) / v >= vec[i].y)
            cnt++;
    return cnt >= n;
}

int main() {
    /*ifstream cin("in.txt");
    ofstream cout("out.txt");
    auto start_time = chrono::high_resolution_clock::now();*/

    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);


    cin >> v >> d >> n;
    vec.assign(n, mp(0, 0));
    max_len = 0;
    for (int i = 0; i < n; i++) {
        string s;
        cin >> vec[i].x >> s;
        max_len = max(max_len, vec[i].x);
        vec[i].y = str_to_int(s);
    }

    double l = 0, r = 24 * 60;
    double eps = 0.1;
    while (l + eps < r) {
        double mid = (l + r) / 2.0;
        if (check(mid))
            r = mid;
        else
            l = mid;
    }
    cout << int_to_str(ceil(round(r) + d * n + (double)(2 * max_len) / v)) << "\n";


    /*auto end_time = chrono::high_resolution_clock::now();
    chrono::duration<double> duration = end_time - start_time;
    cout << duration.count() << "\n";
    cin.close();
    cout.close();*/
    return 0;
}