int main(){
	int i,n,a[10],b[10];
	double c[10],GPA,f;
    GPA=0;
	f=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]<=100 && b[i]>=90){
			c[i]=4.0;}
	    else if(b[i]<=89 && b[i]>=85){
			c[i]=3.7;}
		 else if(b[i]<=84 && b[i]>=82){
			c[i]=3.3;}
 else if(b[i]<=81 && b[i]>=78){
			c[i]=3.0;}
 else if(b[i]<=77 && b[i]>=75){
			c[i]=2.7;}
 else if(b[i]<=74 && b[i]>=72){
			c[i]=2.3;}
 else if(b[i]<=71 && b[i]>=68){
			c[i]=2.0;}
 else if(b[i]<=67 && b[i]>=64){
			c[i]=1.5;}
 else if(b[i]<=63 && b[i]>=60){
			c[i]=1.0;}
 else{c[i]=0;}
	}
 for(i=0;i<n;i++){
GPA+=(a[i]*c[i]);
f+=a[i];
}
GPA/= f;
	 printf("%.2lf",GPA);
	return 0;
		}