#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,a[10005],b[10005];
	int s1=0,s2=0,s3=0;
	cin>>n;
	for(int i=0;i<n;i++)
	{
		cin>>a[i];
		s1+=a[i];
	}
	s1*=3;
	for(int i=0;i<n;i++)
	{
		cin>>b[i];
		s2+=b[i];
	}
	s2*=2;
	for(int i=0;i<n;i++)
	{
		s3+=(a[i]-b[i]);
	}
	double ans=double(double(s1-s2)/s3);
	printf("%.6lf",ans);
	return 0;
}