#include <iostream> 
#include<vector>
#include<algorithm>
#include<map>
#include<iomanip>
#include<set>
#include<queue>
#include<deque>
#include<sstream>
#include<cmath>
#include<bitset>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define req(i,n) for(int i = 1;i <=  n; i++)
#define rrep(i,n) for(int i = n-1;i >= 0;i--)
#define ALL(obj) begin(obj), end(obj)
#define RALL(a) rbegin(a),rend(a)
typedef long long int ll;
typedef long double ld;
template<typename A, size_t N, typename T>
void Fill(A(&array)[N], const T& val) {
    std::fill((T*)array, (T*)(array + N), val);
}
const int MAX = 510000;
const int MOD = 1000000007;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
using p = pair<int, int>;
int main(void) {
    int n,cnt = 0,sum = 0,num=0; cin >> n; vector<int> a(n), b(n);
    rep(i, n) cin >> a[i];
    rep(i, n) cin >> b[i];
    vector<int> c, d;
    sort(ALL(a)); sort(ALL(b));
    d = b;
    do {
        do {
            sum = 0; cnt++;
            rep(i, n) if (a[i] > b[i])sum++;
            if (2 * sum > n) num++;
        } while (next_permutation(ALL(b)));
        b = d;
    } while (next_permutation(ALL(a)));
    cout << fixed << setprecision(10) << (ld)num / cnt << endl;
}