int main(int argc, char* argv[])
{   int n,i;
double c[10],sum1=0,sum2=0,b[10],a[10],GPA;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{scanf("%lf",&a[i]);
	sum2+=a[i];}
    for(i=0;i<n;i++)
	{scanf("%lf",&b[i]);
	if(b[i]>=90&&b[i]<=100)
		c[i]=4.0*a[i];
	else if(b[i]>=85&&b[i]<=89)
		c[i]=3.7*a[i];
	else if(b[i]>=82&&b[i]<=84)
		c[i]=3.3*a[i];
	else if(b[i]>=78&&b[i]<=81)
		c[i]=3.0*a[i];
	else if(b[i]>=75&&b[i]<=77)
		c[i]=2.7*a[i];
	else if(b[i]>=72&&b[i]<=74)
		c[i]=2.3*a[i];
	else if(b[i]>=68&&b[i]<=71)
		c[i]=2.0*a[i];
	else if(b[i]>=64&&b[i]<=67)
		c[i]=1.5*a[i];
	else if(b[i]>=60&&b[i]<=63)
		c[i]=1.0*a[i];
	else if(b[i]<60)
		c[i]=0;
	sum1+=c[i];}
	GPA=sum1/sum2;
	printf("%.2lf",GPA);
	return 0;
}