#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <array>
#include <queue>
#include <stack>
#include <set>
#include <utility>
using namespace std;

int main() {
  int N; cin >> N;
  int A[N]; int B[N];
  for (int i = 0; i < N; i++)
    cin >> A[i];
  for (int i = 0; i < N; i++)
    cin >> B[i];
  vector<int> va;
  for (int i = 1; i <= N; i++) {
    va.push_back(i);
  }

  int gameCount = 0;
  int aWin = 0;
  do {
    vector<int> vb;
    for (int i = 1; i <= N; i++) {
      vb.push_back(i);
    }
    do {
      /*for (int i = 0; i < N; i++)
        cout << va[i];
      cout << " ";
      for (int i = 0; i < N; i++)
        cout << vb[i];
      cout << endl;*/
      int aScore = 0;
      for (int i = 0; i < N; i++) {
        aScore += (A[va[i]-1] > B[vb[i]-1]);
      }
      aWin += (aScore > N/2);
      gameCount++;
    } while (next_permutation(vb.begin(), vb.end()));
  } while (next_permutation(va.begin(), va.end()));
  cout << 1.0 * aWin / gameCount << endl;
}