#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>
using namespace std;
typedef long long LL;
typedef complex<double> CMP;

class LateProfessor { public:
	double getProbability(int waitTime, int walkTime, int lateTime, int bestArrival, int worstArrival) 
	{
		if( worstArrival - bestArrival == 0 )
		{
			int t = bestArrival % (waitTime+walkTime);
			if( t<=waitTime )
				return 0;
			if( t+lateTime <= waitTime+walkTime )
				return 1;
			return 0;
		}

		if( walkTime <= lateTime )
			return 0;

		int bad = 0;
		for(int t=0; t<=worstArrival; t+=waitTime+walkTime)
		{
			int tb = max(bestArrival, t+waitTime);
			int te = min(worstArrival, t+waitTime+walkTime-lateTime);
			if( tb < te )
				bad += te - tb;
		}
		return double(bad) / (worstArrival - bestArrival);
	}
};

// 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(_, LateProfessor().getProbability(waitTime, walkTime, lateTime, bestArrival, worstArrival));}
int main(){

CASE(0)
	int waitTime = 20; 
	int walkTime = 30; 
	int lateTime = 10; 
	int bestArrival = 0; 
	int worstArrival = 50; 
	double _ = 0.4; 
END
CASE(1)
	int waitTime = 20; 
	int walkTime = 30; 
	int lateTime = 10; 
	int bestArrival = 30; 
	int worstArrival = 100; 
	double _ = 0.42857142857142855; 
END
CASE(2)
	int waitTime = 20; 
	int walkTime = 40; 
	int lateTime = 50; 
	int bestArrival = 0; 
	int worstArrival = 300; 
	double _ = 0.0; 
END
CASE(3)
	int waitTime = 101; 
	int walkTime = 230; 
	int lateTime = 10; 
	int bestArrival = 654; 
	int worstArrival = 17890; 
	double _ = 0.6637270828498492; 
END
CASE(4)
	int waitTime = 20; 
	int walkTime = 30; 
	int lateTime = 10; 
	int bestArrival = 90; 
	int worstArrival = 90; 
	double _ = 1.0; 
END
CASE(5)
	int waitTime = 1000; 
	int walkTime = 600; 
	int lateTime = 1; 
	int bestArrival = 17000; 
	int worstArrival = 17000; 
	double _ = 0.0; 
END
CASE(6)
	int waitTime = 1; 
	int walkTime = 2; 
	int lateTime = 1; 
	int bestArrival = 2; 
	int worstArrival = 2; 
	double _ = -1; 
END
CASE(7)
	int waitTime = 1000; 
	int walkTime = 1000; 
	int lateTime = 1000; 
	int bestArrival = 0; 
	int worstArrival = 10000000; 
	double _ = -1; 
END

}
// END CUT HERE
