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