#include <bits/stdc++.h>
using namespace std;

typedef pair<int, int> P;
const int N = 1e4 + 10;

int n, m, hh, mm, ss, service_time;
pair<int, int> persons[N];
priority_queue<int, vector<int>, greater<int> > q;

int main(){
    cin >> n >> m;
    for(int i = 0; i < n; i ++) {
        scanf("%d:%d:%d %d", &hh, &mm, &ss, &service_time);
        service_time = min(60, service_time);
        persons[i] = make_pair(hh * 3600 + mm * 60 + ss, service_time * 60);
    }
    sort(persons, persons+n); // pair默认排序是按first排，相同时按second排序
    for(int i = 0; i < m; i ++) q.push(8 * 3600); // 把m个窗口的开始时间全部安排好

    int sum = 0, cnt = 0;

    for(int i = 0; i < n; i ++){
        int come = persons[i].first, service = persons[i].second;
        int cur_time = q.top(); q.pop(); // 取出堆顶

        if(come > 17 * 3600) break;
        int start_time = max(come, cur_time);
        sum += start_time - come;
        q.push(start_time + service);
        cnt ++;
    }
    printf("%.1lf\n", (double)sum / cnt / 60);
    return 0;
}