#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;

template<typename T>
struct DP2
{
	const int N1, N2;
	vector<T> data;
	DP2(int N1, int N2, const T& t = T())
		: N1(N1), N2(N2), data(N1*N2, t) { assert(data.size()*sizeof(T)<(1<<26)); }
	T& operator()(int i1, int i2)
		{ return data[ (i1*N2)+i2 ]; }
	void swap(DP2& rhs)
		{ data.swap(rhs.data); }
};

class PerfectMemory { public:
	double getExpectation(int N, int M) 
	{
		const int C = N*M;
		DP2<double> dp(C+1, C+1);
		for(int u=0; u<=C; ++u)
			for(int k=0; k<=C; ++k) if( (u+k)%2==0 && k+u<=C )
			{
				if( k > u )
				{
					dp(k,u) = 1 + dp(k-2,u);
				}
				else if( k == u )
				{
					if( k==0 && u==0 )
						dp(k,u) = 0;
					else
						dp(k,u) = 1 + dp(k-1, u-1);
				}
				else // k < u
				{
					dp(k,u) = 1;

					double pFirstIsKnown = double(k) / u;
					double pSecondIsIt = double(1) / (u-1);
					if(k)
						dp(k,u) += pFirstIsKnown * dp(k-1, u-1);
					double pSecondIsThat = double(k) / (u-1);
					dp(k,u) += (1-pFirstIsKnown) * pSecondIsIt * dp(k, u-2);
					dp(k,u) += (1-pFirstIsKnown) * (1-pSecondIsIt-pSecondIsThat) * dp(k+2, u-2);
					dp(k,u) += (1-pFirstIsKnown) * pSecondIsThat * (1 + dp(k, u-2));
				}
//				cerr << k << " " << u << " " << dp(k,u) << endl;
			}
		return dp(0,C);
	}
};

// 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(_, PerfectMemory().getExpectation(N, M));}
int main(){

CASE(0)
	int N = 1; 
	int M = 2; 
	double _ = 1.0; 
END
CASE(1)
	int N = 2; 
	int M = 2; 
	double _ = 2.6666666666666665; 
END
CASE(2)
	int N = 2; 
	int M = 3; 
	double _ = 4.333333333333334; 
END
CASE(3)
	int N = 4; 
	int M = 4; 
	double _ = 12.392984792984793; 
END
/*
CASE(4)
	int N = 50; 
	int M = 50; 
	double _ = -1; 
END
CASE(5)
	int N = 2; 
	int M = 1; 
	double _ = 1.0; 
END
*/
}
// END CUT HERE
