#include <iostream>
using namespace std;
const int N=10;
int a[N],grade[N];
int main() {
int n;
cin>>n;
for(int i=0;i<n;i++) cin>>a[i];
for(int i=0;i<n;i++) cin>>grade[i];
double sum=0;
for(int i=0;i<n;i++){
if(grade[i]>=90) sum+=a[i]*4.0;
else if(grade[i]>=85) sum+=a[i]*3.7;
else if(grade[i]>=82) sum+=a[i]*3.3;
else if(grade[i]>=78) sum+=a[i]*3.0;
else if(grade[i]>=75) sum+=a[i]*2.7;
else if(grade[i]>=72) sum+=a[i]*2.3;
else if(grade[i]>=68) sum+=a[i]*2.0;
else if(grade[i]>=64) sum+=a[i]*1.5;
else if(grade[i]>=60) sum+=a[i]*1.0;
else sum+=0;
}
double k=0;
for(int i=0;i<n;i++) k+=a[i];
printf("%.2lf",sum/k);
return 0;
}