import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		final int[] AS = new int[N];
		final int[] BS = new int[N];
		
		for(int i = 0; i < N; i++){
			AS[i] = sc.nextInt();
		}
		for(int i = 0; i < N; i++){
			BS[i] = sc.nextInt();
		}
		
		ArrayList<Integer> A_random = new ArrayList<Integer>();
		ArrayList<Integer> B_random = new ArrayList<Integer>();
		for(int i = 0; i < N; i++){
			A_random.add(i);
			B_random.add(i);
		}
		
		double answer = Double.NaN;
		for(int i = 0; i < 1000000; i++){
			Collections.shuffle(A_random);
			Collections.shuffle(B_random);
			
			int count = 0;
			for(int j = 0; j < N; j++){
				count += (AS[A_random.get(j)] > BS[B_random.get(j)]) ? 1 : 0;
			}
			
			double prob = (count > N / 2) ? 1 : 0;
			
			if(Double.isNaN(answer)){
				answer = prob;
			}else{
				answer += (prob / i);
				answer *= i;
				answer /= (i + 1);
			}
			//System.out.printf("%d : %.08f\n", i, answer);
		}
		
		System.out.printf("%.08f\n", answer);
	}
	
}