#include <iostream>#include <cstdio>#include<cmath>#include<algorithm>using namespace std;double num[1000000];void init_arrary(){    for (int i = 1; i <= 1000000; ++i)    {        num[i] = num[i - 1] + log(i);    }}double Cn(int m,int n){    return num[m] - num[n] - num[m-n];}int main(){    double n , m;    int i,j;    init_arrary();    while(cin >> n >> m){        double sum=0,res;            res=0;            for(i=1;i<=min(m,n);i++){                sum=Cn(m,i)+Cn(n*m-m,n-i)-Cn(n*m,n);                sum=exp(sum);                 res+=sum*i*i/n;//期望吧            }            cout<<res<<endl;            }    return 0;}