#include <cstdio>
#include <algorithm>
#include <numeric>
#include <vector>
#define repi(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,a) repi(i,0,a)
#define all(a) (a).begin(), (a).end()

int N;
int A[4], B[4];
int cnt, den;

int main()
{
  scanf( "%d", &N );
  rep( i, N )
    scanf( "%d", A+i );
  rep( i, N )
    scanf( "%d", B+i );

  std::vector<int> as(N), bs(N);

  std::iota( all(as), 0 );
  std::iota( all(bs), 0 );

  do
  {
    do
    {
      int a = 0, b = 0;
      rep( i, N )
      {
        if( A[as[i]] > B[bs[i]] )
          ++a;
        else
          ++b;
      } 

      if( a > b )
        ++cnt;

      ++den;
    } while( std::next_permutation( all(bs) ) );
  } while( std::next_permutation( all(as) ) );
  
  printf( "%.6f\n", (double)cnt/den );

  return 0;
}