#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int,int>;

const int N = 4;

int n, a[N], b[N];

int main() {
  cin >> n;
  rep(i, n) cin >> a[i];
  rep(i, n) cin >> b[i];
  sort(b, b + n);
  int numer = 0;
  int denom = 0;
  do {
    int awin = 0;
    rep(i, n) if (a[i] > b[i]) awin++;
    if (2 * awin > n) numer++;
    denom++;
  } while (next_permutation(b, b + n));
  double ans = (double)numer / denom;
  printf("%.2f\n", ans);
  return 0;
}