#include <bits/stdc++.h>
using namespace std;

int a[100],b[100];
int n;
double res,ans,isum,sum;
void check(int x)
{
    if(x >= 90 && x <= 100)  res = 4;
    else if(x >= 85 && x <= 89) res = 3.7;
    else if(x >= 82 && x <= 84) res = 3.3;
    else if(x >= 78 && x <= 81) res = 3; 
    else if(x >= 75 && x <= 77) res = 2.7; 
    else if(x >= 72 && x <= 74) res = 2.3; 
    else if(x >= 68 && x <= 71) res = 2;
    else if(x >= 64 && x <= 67) res = 1.5;
    else if(x >= 60 && x <= 63) res = 1;
    else res = 0;
}
int main()
{
    cin >> n;
    for(int i = 0;i < n;i ++)  
    {
        cin >> a[i];
        isum += a[i];
    }
    for(int i = 0;i < n;i ++)  cin >> b[i];
    for(int i = 0;i < n;i ++)
    {
        check(b[i]);
        ans = res * a[i];
        sum += ans;
    }
    printf("%.2lf",sum / isum);
}