void main()
{
	int i,n,s=0,a[9]={0},b[9]={0};float c[9]={0},d[9]={0},t=0,m;
	scanf("%d",&n);
	for(i=0;i<=n-1;i++)
	{
		scanf("%d",&a[i]);
	}
	for(i=0;i<=n-1;i++)
	{
		scanf("%d",&b[i]);
		if(b[i]<60)
		{c[i]=0;}
		if(b[i]>=60&&b[i]<64)
		{c[i]=1.0;}
		if(b[i]>=64&&b[i]<68)
		{c[i]=1.5;}
		if(b[i]>=68&&b[i]<72)
		{c[i]=2.0;}
		if(b[i]>=72&&b[i]<75)
		{c[i]=2.3;}
		if(b[i]>=75&&b[i]<78)
		{c[i]=2.7;}
		if(b[i]>=78&&b[i]<82)
		{c[i]=3.0;}
		if(b[i]>=82&&b[i]<85)
		{c[i]=3.3;}
		if(b[i]>=85&&b[i]<90)
		{c[i]=3.7;}
		if(b[i]>=90)
		{c[i]=4;}
	}
	for(i=0;i<=n-1;i++)
	{
		d[i]=a[i]*c[i];
		t=t+d[i];
		s=s+a[i];
	}
	m=t/s;
	printf("%.2f",m);
}