import java.io.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.PriorityQueue;

class Main {

    static int ST = 8 * 3600;
    static int ET = 17 * 3600;
    static int MP = 3600;

    static class Client implements Comparable<Client> {
        int at, p;

        public Client(int at, int p) {
            this.at = at;
            this.p = p;
        }

        @Override
        public int compareTo(Client o) {
            return this.at - o.at;
        }
    }

    static int getTime(String ts) {
        String[] s = ts.split(":");
        return Integer.parseInt(s[0]) * 3600 + Integer.parseInt(s[1]) * 60 + Integer.parseInt(s[2]);
    }

    public static void main(String[] args) throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(isr);
        OutputStreamWriter osw = new OutputStreamWriter(System.out);
        BufferedWriter out = new BufferedWriter(osw);
        String[] strs = in.readLine().split(" ");

        int n = Integer.parseInt(strs[0]);
        int k = Integer.parseInt(strs[1]);

        int tn = 0;
        List<Client> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            strs = in.readLine().split(" ");
            int time = getTime(strs[0]);
            if (time > ET) continue;
            Client c = new Client(time, Math.min(Integer.parseInt(strs[1]) * 60, MP));
            list.add(c);
            tn++;
        }
        Collections.sort(list);

        PriorityQueue<Integer> queue = new PriorityQueue<>();
        for (int i = 0; i < k; i++) queue.add(ST);

        int cnt = 0;
        for (int i = 0; i < tn; i++) {
            int st = queue.poll();
            st = Math.max(st, list.get(i).at);
            cnt += st - list.get(i).at;
            int et = st + list.get(i).p;
            queue.add(et);
        }
        out.write(String.format("%.1f", (double) cnt / tn / 60));

        in.close();
        isr.close();
        out.flush();
        out.close();
        osw.close();
    }
}