#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
ll MOD = 1000000007;

const int inf = 1001001001;

int main() {
    int N;
    cin >> N;
    vector<int> A(N);
    vector<int> B(N);
    for (int i = 0; i < N; i++) {
        cin >> A[i];
        A[i]--;
    }
    for (int i = 0; i < N; i++) {
        cin >> B[i];
        B[i]--;
    }
    double all = 0.0;
    int cnt = 0;
    double count = 0.0;
    sort(A.begin(), A.end());
    sort(B.begin(), B.end());
    do{
        do{
            cnt = 0;
            for (int i = 0; i < N; i++) {
                if (A[i] > B[i]) cnt++;
            }
            if (cnt > (N/2)) {
                
                count += 1.0;
            }
            all += 1.0;


        } while(next_permutation(B.begin(), B.end()));

    } while (next_permutation(A.begin(), A.end()));

    
    printf("%.10lf", count/all);
    return 0;
}