
int main(int argc, char* argv[])
{   int n, i, a[10], b[10];   
    double c[10], sum1 = 0, sum2 = 0;
	scanf("%d", &n);
     for(i=0;i<n;i++)
	   {
		   scanf("%d", &a[i]);
           
	 }
	   
	   
         for(i=0;i<n;i++)
	{
	        scanf("%d",&b[i]);
		 
	  
	    if(b[i]>=90)
		      c[i] = 4.0;
	   if(b[i]>=85 && b[i]<=89)
		   c[i] = 3.7;
	   if(b[i]>=82 && b[i]<=84)
		   c[i] = 3.3;
	   if(b[i]>=78 && b[i]<=81)
		   c[i] = 3.0;
	   if(b[i]>=75 && b[i]<=77)
		   c[i] = 2.7;
	   if(b[i]>=72 && b[i]<=74)
		   c[i] = 2.3;
	   if(b[i]>=68 && b[i]<=71)
		   c[i] = 2.0;
	   if(b[i]>=64 && b[i]<=67)
		   c[i] = 1.5;
	   if(b[i]>=60 && b[i]<=63)
		   c[i] = 1.0;
	   if(b[i]<60)
		   c[i] = 0;
	   
	   sum2 += a[i] * c[i];
	   sum1 += a[i];
	 }
	printf("%.2f", sum2 / sum1);
	return 0;
}