#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int main()
{
    int f, n, k;
    cin >> f >> n >> k;

    double ans = 0.0;
    for(int x=1; x<=f; ++x){
        vector<vector<double> > dp(n+1, vector<double>(n+1, 0.0));
        dp[0][0] = 1.0;
        for(int i=0; i<n; ++i){
            vector<vector<double> > nextDp(n+1, vector<double>(n+1, 0.0));
            for(int a=0; a<n; ++a){
                for(int b=0; b<n; ++b){
                    nextDp[a][b]   += dp[a][b] * (1.0 / f);
                    nextDp[a+1][b] += dp[a][b] * ((x - 1.0) / f);
                    nextDp[a][b+1] += dp[a][b] * ((f - x) / (double)f);
                }
            }
            dp.swap(nextDp);
        }
        for(int a=0; a<=n-k; ++a){
            for(int b=0; b<k; ++b){
                ans += dp[a][b] * x;
            }
        }
    }
    printf("%.10f\n", ans);

    return 0;
}