void main()
{
	int i,n,a[101],b[101],sum=0;
	float gpa=0;
	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){
		gpa+=4*a[i];	
		}
		else if(b[i]>=85&&b[i]<=89){

			gpa+=3.7*a[i];
		}
		else if(b[i]>=82&&b[i]<=84){
			gpa+=3.3*a[i];
		}
		else if(b[i]>=78&&b[i]<=81){
			gpa+=3.0*a[i];
		}
		else if(b[i]>=75&&b[i]<=77){
			gpa+=2.7*a[i];
		}
		else if(b[i]>=72&&b[i]<=74){
			gpa+=2.3*a[i];
		}
		else if(b[i]>=68&&b[i]<=71){
			gpa+=2.0*a[i];
		}
		else if(b[i]>=64&&b[i]<=67){
			gpa+=1.5*a[i];
		}
		else if(b[i]>=60&&b[i]<=63){
			gpa+=1.0*a[i];
		}
	}
	for(i=0;i<n;i++){
		sum+=a[i];
	}
	printf("%.2f\n",gpa/sum);
}
