import java.util.Scanner;
public class Main{
	static int[] a1;
	static int[] b1;
	static double sum1;
	static boolean[] a2;
	static int n;
	static int[] a3;
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		sum1=0;
		a1=new int[n];
		b1=new int[n];
		a2=new boolean[n];
		a3=new int[n];
		double sum=1;
		for(int i = 0; i<n; i++){
			int a = sc.nextInt();
			a1[i]=a;
		}
		for(int i = 0; i<n; i++){
			int b = sc.nextInt();
			b1[i]=b;
		}
		for(int i=2; i<=n; i++){
			sum*=i;
		}
		dfs(n-1);
		System.out.println(sum1/sum);
	}
	static void dfs(int k){
		for(int i=0; i<n; i++){
			if(!a2[i]){
				a3[k]=a1[i];
				a2[i]=true;
				dfs(k-1);
				a2[i]=false;
			}
		}
		if(k==0){
			if(judge(a3)){
				sum1++;
			}
		}
	} 
	
	static boolean judge(int[] c){
		int win=0;
		for(int i = 0; i<n; i++){
			if(c[i]>b1[i]){
				win++;
			}
		}
		if(win>(n/2)){
			return true;
		}else{
			return false;
		}
	}
}