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

