void main()
{
	int a[10],b[10],i,n,m=0;
	float c[10],y,sum=0;
	scanf("%d\n",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d ",&a[i]);
	}
	scanf("\n");
	for(i=0;i<n;i++)
	{
		scanf("%d ",&b[i]);
	}
	for(i=0;i<n;i++)
	{
		if (b[i]>=90) 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 if(b[i]<60) c[i]=0;
	}
	for(i=0;i<n;i++)
	{
		sum=sum+a[i]*c[i];
		m=m+a[i];
	}
	y=sum/m;
	printf("%.2f",y);
}
		