#include<bits/stdc++.h>
using namespace std;
long long a[1005],b[1005];
int main(){
	long long n;
	double ans1=0,ans2=0;
	scanf("%lld",&n);
	for(int i=1;i<=n;++i){scanf("%lld",&a[i]);ans1+=a[i];}
	for(int i=1;i<=n;++i){scanf("%lld",&b[i]);ans2+=b[i];}
	printf("%.6lf",(ans1*3-ans2*2)/(ans1-ans2));
	return 0;
}