int main()
{
 int n,i,s=0;
 scanf("%d",&n);
 printf("\n");
 int a[n],b[n];
 double c[n],sum=0,x;
 for(i=0;i<n;i++)
 {
  scanf("%d ",&a[i]);
  s=s+a[i];
 }
 printf("\n");
 for(i=0;i<n;i++)
 {
  scanf("%d ",&b[i]);
  if(b[i]>89) c[i]=4.0;
  else if(b[i]>84) c[i]=3.7;
  else if(b[i]>81) c[i]=3.3;
  else if(b[i]>77) c[i]=3.0;
  else if(b[i]>74) c[i]=2.7;
  else if(b[i]>71) c[i]=2.3;
  else if(b[i]>67) c[i]=2.0;
  else if(b[i]>63) c[i]=1.5;
  else if(b[i]>59) c[i]=1.0;
  else c[i]=0;
  sum=sum+c[i]*a[i];
 }
  printf("\n");
  x=sum/s;
  printf("%.2lf\n",x);
  return 0;
}
 
 