#include<cstdio>
#include<algorithm>
using namespace std;

int n, a[4], b[4];

int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", &a[i]);
  for (int i = 0; i < n; i++) scanf("%d", &b[i]);
  int win = 0, counter = 0;
  sort(a, a+n);
  sort(b, b+n);
  do {
    do {
      counter++;
      int temp = 0;
      for (int i = 0; i < n; i++) if (a[i] > b[i]) temp++;
      if (temp * 2 > n) win++;
    } while (next_permutation(b, b+n));
  } while (next_permutation(a, a+n));
  printf("%f\n", (double)win / counter);
}