#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;
}