int main ()
{
 int n,i=0,a[N],b[N],x=0;
 float c[N],y=0.0,z;
 scanf("%d",&n);
 for(i=0;i<n;i++)
  scanf("%d",&a[i]);
 for(i=0;i<n;i++)
  scanf("%d",&b[i]);
 for(i=0;i<n;i++)
 {
  if(b[i]>=90&&b[i]<=100) c[i]=4.0;
  else if(b[i]>=90&&b[i]<=100) c[i]=4.0;
  else if(b[i]>=85&&b[i]<=89) c[i]=3.7;
  else if(b[i]>=82&&b[i]<=83) c[i]=3.3;
  else if(b[i]>=78&&b[i]<=81) c[i]=3.0;
  else if(b[i]>=75&&b[i]<=77) c[i]=2.7;
  else if(b[i]>=72&&b[i]<=73) c[i]=2.3;
  else if(b[i]>=68&&b[i]<=71) c[i]=2.0;
  else if(b[i]>=64&&b[i]<=67) c[i]=1.5;
  else if(b[i]>=60&&b[i]<=63) c[i]=1.0;
  else if(b[i]<=59) c[i]=0.0;
 }
 for(i=0;i<n;i++)
 {
	 y=y+a[i]*c[i];
	 x=x+a[i];
 }
 z=y/x;
 printf("%.2f",z);
}


