int main()
{
	int a[10],n,i,sum=0;
	double b[10],num=0,c[10];
	scanf("%d",&n);
	for(i=0;i<n;i++){
		cin>>a[i];
	}
	for(i=0;i<n;i++){
	cin>>b[i];
	}
	for(i=0;i<n;i++){
		if(b[i]>=90&&b[i]<=100) {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;}
	}
	
    for(i=0;i<n;i++){
		sum+=a[i];
	}

	for(i=0;i<10;i++){
		num+=c[i]*a[i];
	}
   
	printf("%0.2f\n",num/sum);
	
	return 0;
}

 

 
