#include<bits/stdc++.h>
using namespace std;
struct coffe
{
	double time,deli;
	double rate;	
}node[100010];
void quick_sort(int l,int r)
{
	if(l>=r) return;
	double x = node[l].rate;
	int i = l-1,j = r+1;
	while(i<j)
	{
		do{
			i++;
		}while(node[i].rate>x);
		do{
			j--;
		}while(node[j].rate<x);
		if(i<j) 
		{
			coffe p = node[j];
			node[j] = node[i];
			node[i] = p;
		}
	}
	quick_sort(l,j);quick_sort(j+1,r);
}
int main()
{
	int n,m;cin>>n>>m;
	for(int i=0;i<n;i++) cin>>node[i].deli;
	for(int i=0;i<n;i++) cin>>node[i].time;
	for(int i=0;i<n;i++) node[i].rate = (double)node[i].deli/node[i].time;
	quick_sort(0,n-1);
	double del=0,ti=0;
	for(int i=0;i<m;i++) del+=node[i].deli,ti+=node[i].time;
	printf("%.3f",del/ti); 
	return 0;
}