pat 1017

#include<iostream>
#include<algorithm>
#include<stdio.h>
using namespace std;
struct client{
	double arrive_time;
	double deal_time;
	bool operator<(const client &b) const{
		return arrive_time<b.arrive_time;
	}
};
int main(){
	freopen("C:\\Users\\Frank Wang\\Desktop\\in.txt","r",stdin);
	const int N=10001;
	int n,k;
	double q[N];
	client a[N];
	cin>>n>>k;
	for(int i=0;i<n;i++){
		int hh,mm,ss;
		//char c1,c2;
		scanf("%d:%d:%d%lf",&hh,&mm,&ss,&a[i].deal_time);
		//cin>>hh>>c1>>mm>>c2>>ss>>a[i].deal_time;
		a[i].arrive_time=hh*60.0+(double)mm+ss/60.0;
	}
	sort(a,a+n);
//	for(int i=0;i<n;i++){
//		cout<<a[i].arrive_time<<' '<<a[i].deal_time<<endl;
//	}
	for(int i=0;i<k;i++){
		q[i]=480.0;
	}
	double sum=0;
	bool flag;
	int j;
	int nw=0;
	for(int i=0;i<n;i++){
		if(a[i].arrive_time>1020.0) break;
		++nw;
		flag=1;
		if(a[i].arrive_time<480.0){
			sum+=480.0-a[i].arrive_time;
			a[i].arrive_time=480.0;
		}
		
		double min=10200;
		for(int ii=0;ii<k;ii++){
			if(q[ii]<=a[i].arrive_time){
				q[ii]=a[i].arrive_time+a[i].deal_time;
				flag=0;
				break;
			}
			if(min>q[ii]) {min=q[ii];j=ii;}
		}
		if(flag){
			sum+=q[j]-a[i].arrive_time;
			q[j]+=a[i].deal_time;
		}
	}
//	cout<<sum<<endl;
//	cout<<nw<<endl;
//	cout<<sum/nw<<endl;
	printf("%.1lf\n",sum/nw);
}