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

