#include <algorithm>

#include <bitset>

#include <cctype>

#include <cerrno>

#include <clocale>

#include <cmath>

#include <complex>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <ctime>

#include <deque>

#include <exception>

#include <fstream>

#include <functional>

#include <limits>

#include <list>

#include <map>

#include <iomanip>

#include <ios>

#include <iosfwd>

#include <iostream>

#include <istream>

#include <ostream>

#include <queue>

#include <set>

#include <sstream>

#include <stdexcept>

#include <streambuf>

#include <string>

#include <utility>

#include <vector>

#include <cwchar>

#include <cwctype>

#include <stack>

#include <limits.h>

using namespace std;

#define MAXN 1010

int i,j,n,s;

double f[MAXN][MAXN];

int main()

{

        while (scanf("%d%d",&n,&s) != EOF)

        {

                memset(f,,sizeof(f));

                f[n][s] = ;

                for (i = n; i >= ; i--)

                {

                        for (j = s; j >= ; j--)

                        {

                                if (i == n && j == s) continue;

                                f[i][j] = (1.0 * i * (s - j) * f[i][j+] + 1.0 * (n - i) * j * f[i+][j] + 1.0 * (n - i) * (s - j) * f[i+][j+] + n * s) / (n * s - i * j);

                        }

                }

                printf("%.4lf\n",f[][]);

        }

        return ;

}