void main()
{
	int a[11],b[11];
	int g=0,i,n;
	float GPA,c[11],f=0,d[11];
	scanf("%d",&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)
			c[i]=4.0;
		else if(b[i]>=85)
			c[i]=3.7;
		else if(b[i]>=82)
			c[i]=3.3;
		else if(b[i]>=78)
			c[i]=3.0;
		else if(b[i]>=75)
			c[i]=2.7;
		else if(b[i]>=72)
			c[i]=2.3;
		else if(b[i]>=68)
			c[i]=2.0;
		else if(b[i]>=64)
			c[i]=1.5;
		else if(b[i]>=60)
			c[i]=1.0;
		else
			c[i]=0;
	}
	for(i=0;i<n;i++)
	{
		d[i]=c[i]*a[i];
		f=f+d[i];
		g=g+a[i];
	}
	GPA=(float)f/g;
	printf("%.2f\n",GPA);
}
