void main()
{
	int i,j=0,k=0,n,a[10]={0},b[10]={0};
    float c[10]={0.0},s=0.0,total=0.0;
	scanf("%d\n",&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<10;i++)
            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]<=84)
			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]<=74)
			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]<60)
			c[i]=0.0;
      for (i=0;i<n;i++)
		  s=s+a[i]*c[i];
	  for (i=0;i<n;i++)
		  total=total+a[i];
	  s=s/total;
	  printf("%.2f",s);
}
