void main()
{
	int n,i,b[10];
	double a[10],c[10],GPA,sum1=0,sum2=0;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%lf",&a[i]);
	}
	for(i=0;i<=n;i++)
	{
		scanf("%d",&b[i]);
	}
	for(i=0;i<n;i++)
	{
		if(b[i]<=100&&b[i]>=90)
			c[i]=4.0*a[i];
		else if(b[i]>=85)
			c[i]=3.7*a[i];
		else if(b[i]>=82)
			c[i]=3.3*a[i];
		else if(b[i]>=78)
			c[i]=3.0*a[i];
		else if(b[i]>=75)
			c[i]=2.7*a[i];
		else if(b[i]>=72)
			c[i]=2.3*a[i];
		else if(b[i]>=68)
			c[i]=2.0*a[i];
		else if(b[i]>=64)
			c[i]=1.5*a[i];
		else if(b[i]>=60)
			c[i]=1.0*a[i];
		else
			c[i]=0;
	}
	for(i=0;i<n;i++)
	{
		sum1=sum1+c[i];
		sum2=sum2+a[i];
	}
	GPA=sum1/sum2;
	printf("\n%.2lf\n",GPA);
}