void main()
{
	int n,c[100],x[100],i,k,sum=0;
	double j[100],gpa=0,GPA;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d",&x[i]);
	}
	for(i=0;i<n;i++)
	{
		scanf("%d",&c[i]);
	}
	for(i=0;i<n;i++)
	{
		if(c[i]<=100&&c[i]>89)
			j[i]=4.0;
		else if(c[i]<=89&&c[i]>84)
			j[i]=3.7;
		else if(c[i]<=84&&c[i]>81) 
			j[i]=3.3;
		else if(c[i]<=81&&c[i]>77)
			j[i]=3.0;
		else if(c[i]<=77&&c[i]>74)
			j[i]=2.7;
		else if(c[i]<=74&&c[i]>71)
			j[i]=2.3;
								else if(c[i]<=71&&c[i]>67)
									j[i]=2.0;
								else if(c[i]<=67&&c[i]>63)
									j[i]=1.5;
								else if(c[i]<=63&&c[i]>59)
									j[i]=1.0;
								else
									j[i]=0;
								gpa+=(double)j[i]*x[i];
								sum+=x[i];
	}
	GPA=gpa/sum;
	printf("%.2lf",GPA);
}
