int main()
{
	int n,i;
	double a[10],b[10],c[10],d[10],D=0,A=0,GPA;
	cin>>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++){
		d[i]=a[i]*c[i];}
	for(i=0;i<n;i++){
		D+=d[i];
		A+=a[i];}
	GPA=D/A;
	printf("%.2f\n",GPA);
	return 0;
}