int main(){
	int n,i,a[10],b[10];
	float c[10],d[10];
	int p=0;
	float gpa,q=0;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d",&a[i]);
		p+=a[i];
	}
	for(i=0;i<n;i++){
		scanf("%d",&b[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];
		q+=d[i];
	}
	gpa=q/p;
	printf("%.2f",gpa);
	return 0;
}
