#include <iostream>
#include <string>
#include <algorithm>
#include <cstdio>

using namespace std;

const int N = 10;

int n;
int a[N], b[N];
float c[N];//a[i]为学分,b[i]为得分,c[i]为绩点
float GPA;
int sum;

int main() {
    cin >> n;
    for (int i = 0; i < n; i++) cin >> a[i];
    for (int i = 0; i < n; i++) {
       cin >> b[i];
       if (b[i] >= 90) c[i] = 4.0;
       else if (b[i] >= 85) c[i] = 3.7;
       else if (b[i] >= 82) c[i] = 3.3;
       else if (b[i] >= 78) c[i] = 3.0;
       else if (b[i] >= 75) c[i] = 2.7;
       else if (b[i] >= 72) c[i] = 2.3;
       else if (b[i] >= 68) c[i] = 2.0;
       else if (b[i] >= 64) c[i] = 1.5;
       else if (b[i] >= 60) c[i] = 1.0;
       else c[i] = 0;
    }
    for (int i = 0; i < n; i++) {
        GPA +=(a[i] * c[i]);
        sum += a[i];
    }
    GPA = GPA / sum;
    printf("%.2f", GPA);
    return 0;
}