void main()
{
	int n,i,k,t,a[2][10];
	float sum ;
	scanf("%d",&n);
	for(k=0;k<2;k++)
	for (i=0;i<n;i++)
		scanf("%d",&a[k][i]);
 
	sum=0;
	for (i=0;i<n;i++)
	{
		if (a[1][i]<=100&&a[1][i]>=90)
			sum=sum+4.0*a[0][i];
		else if (a[1][i]<=89&&a[1][i]>=85)
			sum=sum+3.7*a[0][i];
		else if (a[1][i]<=84&&a[1][i]>=82)
			sum=sum+3.3*a[0][i];
		else if (a[1][i]<=81&&a[1][i]>=78)
			sum=sum+3.0*a[0][i];
        else if (a[1][i]<=77&&a[1][i]>=75)
			sum=sum+2.7*a[0][i];
		else if (a[1][i]<=74&&a[1][i]>=72)
			sum=sum+2.3*a[0][i];
		else if (a[1][i]<=71&&a[1][i]>=68)
			sum=sum+2.0*a[0][i];
	   else 	if (a[1][i]<=67&&a[1][i]>=64)
			sum=sum+1.5*a[0][i];
        else	if (a[1][i]<=63&&a[1][i]>=60)
			sum=sum+1.0*a[0][i];
	else 	if (a[1][i]<=60 )
			sum=sum ;
	}
	t=0;
	for (i=0;i<n;i++)
		t=t+a[0][i];
	sum=sum/t;
	printf("%.2f",sum);
}

