#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 <cstring>
#ifdef __GNUC__
#include <ext/hash_map>
#define unordered_map __gnu_cxx::hash_map
#else
#include <unordered_map>
#endif
using namespace std;
typedef long long LL;
typedef complex<double> CMP;
class MagicBlizzard { public:
double expectation(vector <int> range, vector <int> amount)
{
vector< pair<int,int> > ar;
for(int i=0; i<range.size(); ++i)
ar.push_back(make_pair(range[i], amount[i]));
sort(ar.begin(), ar.end());
double total = 0.0;
int cnt = 0;
for(int i=0; i<ar.size(); ++i)
for(int _=0; _<ar[i].second; ++_)
total += 2.0 * (cnt++) / (ar[i].first*2+1) / (ar[i].first*2+1) + 1;
return total;
}
};
// 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(_, MagicBlizzard().expectation(range, amount));}
int main(){
CASE(0)
int range_[] = {1,0};
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = {1,1};
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = 2.2222222222222223;
END
CASE(1)
int range_[] = {1,0};
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = {2,1};
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = 3.666666666666667;
END
CASE(2)
int range_[] = {5,2,6,5};
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = {1,2,2,3};
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = 8.46525111252384;
END
CASE(3)
int range_[] = {7,11,2,13,3,19,5,17};
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = {16,8,4,15,12,9,10,6};
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = 98.55659436211914;
END
CASE(4)
int range_[] = {0,0,0,0,0,0,0,0,0,0};
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = {10000,10000,10000,10000,10000,10000,10000,10000,10000,10000};
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = 1.0E10;
END
/*
CASE(5)
int range_[] = ;
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = ;
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = ;
END
CASE(6)
int range_[] = ;
vector <int> range(range_, range_+sizeof(range_)/sizeof(*range_));
int amount_[] = ;
vector <int> amount(amount_, amount_+sizeof(amount_)/sizeof(*amount_));
double _ = ;
END
*/
}
// END CUT HERE