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