#include <iostream>
#include <sstream>
#include <iomanip>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
#include <iterator>
#include <functional>
#include <complex>
#include <queue>
#include <stack>
#include <cmath>
#include <cassert>
#include <tuple>
using namespace std;
typedef long long LL;
typedef complex<double> CMP;
class GreaterGame { public:
double calc(vector <int> hand, vector <int> sothe)
{
const int N = hand.size();
set<int> me, you, rest;
for(int c=1; c<=2*N; ++c) rest.insert(c);
for(int c: hand) me.insert(c), rest.erase(c);
for(int c: sothe) you.insert(c), rest.erase(c);
double ans = 0.0;
while(!you.empty() && *you.rbegin()>0)
{
int y = *you.rbegin(); you.erase(y);
auto it = me.rbegin();
if(*it > y) {
while(*it>y) {
auto kt = it;
++kt;
if(kt==me.rend() || *kt<y)
break;
it = kt;
}
me.erase(*it);
++ans;
} else {
me.erase(me.begin());
}
}
for(int c: me)
ans += count_if(rest.begin(), rest.end(), [&](int y){return y<c;}) / (double)rest.size();
return ans;
}
};
// BEGIN CUT HERE
#include <ctime>
double start_time; string timer()
{ ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
{ os << "{ ";
for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
void verify_case(const double& Expected, const double& Received) {
bool ok = (abs(Expected - Received) < 1e-9);
if(ok) cerr << "PASSED" << timer() << endl; else { cerr << "FAILED" << timer() << endl;
cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
#define END verify_case(_, GreaterGame().calc(hand, sothe));}
int main(){
CASE(0)
int hand_[] = {4,2};
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = {-1,-1};
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = 1.5;
END
CASE(1)
int hand_[] = {4,2};
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = {1,3};
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = 2.0;
END
CASE(2)
int hand_[] = {2};
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = {-1};
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = 1.0;
END
CASE(3)
int hand_[] = {1,3,5,7};
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = {8,-1,4,-1};
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = 2.5;
END
CASE(4)
int hand_[] = {6,12,17,14,20,8,16,7,2,15};
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = {-1,-1,4,-1,11,3,13,-1,-1,18};
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = 8.0;
END
/*
CASE(5)
int hand_[] = ;
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = ;
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = ;
END
CASE(6)
int hand_[] = ;
vector <int> hand(hand_, hand_+sizeof(hand_)/sizeof(*hand_));
int sothe_[] = ;
vector <int> sothe(sothe_, sothe_+sizeof(sothe_)/sizeof(*sothe_));
double _ = ;
END
*/
}
// END CUT HERE