void main()
{
	int n,a[10],i,c[10],sum2=0;
	double b[10],GPA,sum1=0;
	scanf("%d",&n);
	for(i=0;i<=n-1;i++)
	{
		scanf("%d",&a[i]);
	}
	for(i=0;i<=n-1;i++)
	{
		scanf("%d",&c[i]);
	}
	for(i=0;i<=n-1;i++)
	{
		if(c[i]>=90)b[i]=4.0;
		else
		{if(c[i]>=85)b[i]=3.7;
		else
		{if(c[i]>=82)b[i]=3.3;
		else
		{if(c[i]>=78)b[i]=3.0;
		else
		{if(c[i]>=75)b[i]=2.7;
		else
		{if(c[i]>=72)b[i]=2.3;
		else
		{if(c[i]>=68)b[i]=2.0;
		else
		{if(c[i]>=64)b[i]=1.5;
		else
		{if(c[i]>=60)b[i]=1.0;
		else b[i]=0;
		}
		}
		}
		}
		}
		}
		}
		}
	}
for(i=0;i<=n-1;i++)
{
sum1=sum1+a[i]*b[i];
sum2=sum2+a[i];
}
GPA=sum1/sum2;
printf("%.2f\n",GPA);
}