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

     