problem FFFFFUUUUUU

#include <iostream>
#include <fstream>
#include <cstdio>
#include <iomanip>
#include <sstream>
#include <cstring>
#include <string>
#include <cmath>
#include <stack>
#include <list>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <vector>
#include <algorithm>
#include <numeric>
#include <utility>
#include <functional>
#include <limits>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;

const double pi = acos(-1.0);

#define oned(a, x1, x2) { cout << #a << ":"; for(int _i = (x1); _i < (x2); _i++){ cout << " " << a[_i]; } cout << endl; }
#define twod(a, x1, x2, y1, y2) { cout << #a << ":" << endl; for(int _i = (x1); _i < (x2); _i++){ for(int _j = (y1); _j < (y2); _j++){ cout << (_j > y1 ? " " : "") << a[_i][_j]; } cout << endl; } }
#define mp(x, y) make_pair(x, y)

int n, m;
double dp[1000005], psum[1000005];

void solve() {
    for(int i = n; i <= n*m; i++) {
        dp[i] = i*1./n;
    }

    for(int k = n-1; k > 0; k--) {
        for(int i = 0; i < n*m; i++) {
            psum[i+1] = dp[i+1]+psum[i];
        }

        double ik = 1./k, im = 1./m;
        for(int i = k; i <= n*m; i++) {
            dp[i] = max(i*ik, (psum[min(n*m,i+m)]-psum[i])*im);
        }
    }

    double res = 0;
    for(int i = 1; i <= m; i++) {
        res += dp[i];
    }
    cout << fixed << setprecision(12);
    cout << res / m << endl;
}

int main() {
//  freopen("F.in", "r", stdin);
    while(cin >> n >> m) {
        solve();
    }
}