void main()
{
	int a[10],b[10],m=0,n,i;float c[10],GPA,sum=0.0;
	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&&b[i]<=100)c[i]=a[i]*4.0;
if(b[i]>=85&&b[i]<=89)c[i]=a[i]*3.7;
if(b[i]>=82&&b[i]<=84)c[i]=a[i]*3.3;
if(b[i]>=78&&b[i]<=81)c[i]=a[i]*3.0;	
if(b[i]>=75&&b[i]<=77)c[i]=a[i]*2.7;
if(b[i]>=72&&b[i]<=74)c[i]=a[i]*2.3;
if(b[i]>=68&&b[i]<=71)c[i]=a[i]*2.0;
if(b[i]>=64&&b[i]<=67)c[i]=a[i]*1.5;
if(b[i]>=60&&b[i]<=63)c[i]=a[i]*1.0;
if(b[i]<60)c[i]=0.0;
	}
for(i=0;i<n;i++)
{
	sum+=c[i];
m+=a[i];
}
GPA=sum/m;
printf("%.2f",GPA);
}