#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define pb(a) push_back(a)
#define pr(a) cout<<(a)<<endl
#define PR(a,b) cout<<(a)<<" "<<(b)<<endl
#define R cin>>
#define F first
#define S second
#define ll long long
bool check(int n,int m,int x,int y){return (x<0||x>=n||y<0||y>=m)?false:true;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
typedef pair<int,int> P;

int main() {
  int n;
  cin >> n;
  int a[n],b[n];
  rep(i,n) cin >> a[i];
  rep(i,n) cin >> b[i];
  double win=0,sum=0;
  sort(a,a+n);
  do {
    sort(b,b+n);
    do {
      int cnt=0;
      for(int i=0; i<n; i++) {
	if(a[i]>b[i]) cnt++;
      }
      if(cnt>n/2) win+=1;
      sum+=1;
    } while(next_permutation(b,b+n));
  } while(next_permutation(a,a+n));
  cout << win/sum << endl;
  return 0;
}