
int main(){
	int xf[10];
	int cj[10];
	double gd[10];
	int i,n;
	double GPA;
	double zgd=0;
	double zxf=0;

	scanf("%d",&n);

	for(i=0;i<n;i++){
		scanf("%d",&(xf[i]));
	}

	for(i=0;i<n;i++){
		scanf("%d",&(cj[i]));
	}

	for(i=0;i<n;i++){
		if(cj[i]>=90&&cj[i]<=100){
			gd[i]=4.0*xf[i];
		}
		else if(cj[i]>=85&&cj[i]<=89){
			gd[i]=3.7*xf[i];
		}
		else if(cj[i]>=82&&cj[i]<=84){
			gd[i]=3.3*xf[i];
		}
		else if(cj[i]>=78&&cj[i]<=81){
			gd[i]=3.0*xf[i];
		}
		else if(cj[i]>=75&&cj[i]<=77){
			gd[i]=2.7*xf[i];
		}
		else if(cj[i]>=72&&cj[i]<=74){
			gd[i]=2.3*xf[i];
		}
		else if(cj[i]>=68&&cj[i]<=71){
			gd[i]=2.0*xf[i];
		}
		else if(cj[i]>=64&&cj[i]<=67){
			gd[i]=1.5*xf[i];
		}
		else if(cj[i]>=60&&cj[i]<=63){
			gd[i]=1.0*xf[i];
		}
		else{
			gd[i]=0.0;
		}
	}

	for(i=0;i<n;i++){
		zxf+=1.0*xf[i];
	}

	for(i=0;i<n;i++){
		zgd+=gd[i];
	}

	GPA=zgd/zxf;

	printf("%.2lf",GPA);

	return 0;

}