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