void main()
{
int n,a[11],b[11],i;float GPA,c[11],d[11],P=0,Q=0;
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) c[i]=4.0;
 else if(b[i]>=85) c[i]=3.7;
 else if(b[i]>=82) c[i]=3.3;
else if(b[i]>=78) c[i]=3.0;
else if(b[i]>=75) c[i]=2.7;
else if(b[i]>=72) c[i]=2.3;
else if(b[i]>=68) c[i]=2.0;
else if(b[i]>=64) c[i]=1.5;
else if(b[i]>=60) c[i]=1.0;
else c[i]=0;
}
for(i=0;i<n;i++)
 d[i]=a[i]*c[i];
for(i=0;i<n;i++)
P=P+d[i];
for(i=0;i<n;i++)
Q=Q+a[i];
GPA=P/Q;
printf("%.2f\n",GPA);
}