import java.util.*;

public class Exercise143{
  public static double winGames;
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int[] a = new int[n];
    ArrayList<Integer> b = new ArrayList<Integer>();
    for(int i = 0; i < n; i++){
      a[i] = sc.nextInt();
    }
    for(int i = 0; i < n; i++){
      b.add(sc.nextInt());
    }
    double sumGames = 1;
    winGames = 0;

    for(int i = 0; i < n; i++){
      sumGames *= n - i;
    }
    permute(n, a, b, 0);

    System.out.println(winGames / sumGames);
  }
  private static void permute (int n, int[] a, ArrayList<Integer> b, int k){
    for(int i = k; i < b.size(); i++){
      Collections.swap(b, i, k);
      permute(n, a, b, k + 1);
      Collections.swap(b, k, i);
    }
    if(k == b.size() - 1){
      if(judge(n, a, b)){
        winGames++;
      }
    }
  }
  private static boolean judge (int n, int[] a, ArrayList<Integer> b){
    int win = 0;
    for(int i = 0; i < n; i++){
      if(a[i] > b.get(i)){
        win++;
      }
    }
    if(win > n / 2){
      return true;
    }else{
      return false;
    }
  }
}