int main(){
	int a[100],b[100],n,i,s,xfh=0;
	double jd,jdh=0,gpa;
	scanf("%d\n",&n);
	for(i=0;i<n;i++){
		scanf("%d",&a[i]);
		xfh+=a[i];
	}
	for(s=0;s<n;s++){
		scanf("%d",&b[s]);
		if ((b[s]<=100)&&(b[s]>=90)){
			jd=4.0*a[s];
		}else if ((b[s]<=89)&&(b[s]>=85)){
			jd=3.7*a[s];
		}else if ((b[s]<=84)&&(b[s]>=82)){
			jd=3.3*a[s];
		}else if ((b[s]<=81)&&(b[s]>=78)){
			jd=3.0*a[s];
		}else if ((b[s]<=77)&&(b[s]>=75)){
			jd=2.7*a[s];
		}else if ((b[s]<=74)&&(b[s]>=72)){
			jd=2.3*a[s];
		}else if ((b[s]<=71)&&(b[s]>=68)){
			jd=2.0*a[s];
		}else if ((b[s]<=67)&&(b[s]>=64)){
			jd=1.5*a[s];
		}else if ((b[s]<=63)&&(b[s]>=60)){
			jd=4.0*a[s];
		}else{
			jd=0.0;
		}
		jdh+=jd;
	}
	gpa=jdh/xfh;
	printf ("%.2lf",gpa);
	return 0;
}