int main()
{
    int n,i;
    double sum,GPA,temp;
    scanf("%d",&n);
    int d[n];
    double c[n],b[n],a[n];
    for(i=1;i<=n;i++)
    {
                     scanf("%lf",&a[i]);
                     }
    for(i=1;i<=n;i++)
    {
                     scanf("%d",&d[i]);
                     }
    for(i=1;i<=n;i++)
    {
                     if(d[i]<=100&&d[i]>=90)
                     {
                                            b[i]=4.0;
                                            }
                     if(d[i]<=89&&d[i]>=85)
                     {
                                            b[i]=3.7;
                                            }
                     if(d[i]<=84&&d[i]>=82)
                     {
                                            b[i]=3.3;
                                            }
                     if(d[i]<=81&&d[i]>=78)
                     {
                                            b[i]=3.0;
                                            }
                     if(d[i]<=77&&d[i]>=75)
                     {
                                            b[i]=2.7;
                                            }
                     if(d[i]<=74&&d[i]>=72)
                     {
                                            b[i]=2.3;
                                            }
                     if(d[i]<=71&&d[i]>=68)
                     {
                                            b[i]=2.0;
                                            }
                     if(d[i]<=67&&d[i]>=64)
                     {
                                            b[i]=1.5;
                                            }
                     if(d[i]<=63&&d[i]>=60)
                     {
                                            b[i]=1.0;
                                            }
                     if(d[i]<60)
                     {
                                b[i]=0;
                                            }
    }
    for(i=1;i<=n;i++)
    {
                     c[i]=a[i]*b[i];
                     }
    sum=0;
    temp=0;
    for(i=1;i<=n;i++)
    {
                      sum=sum+a[i];
                      }
    for(i=1;i<=n;i++)
    {
                     temp=temp+c[i];
                     }
    GPA=temp/sum;
    printf("%.2lf",GPA);
    return 0;
}