//#pragma GCC target("avx2")
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using pli = pair<ll,int>;
#define TEST cerr << "TEST" << endl
#define AMARI 998244353
//#define AMARI 1000000007
#define el '\n'
#define El '\n'

long double binom(int n,int k){
    long double ans = 1;
    int bunsi = n,bunbo = 1;
    for(int i = 0; i < k; i++){
        ans *= (long double)bunsi;
        ans /= (long double)bunbo;
        bunsi--; bunbo++;
    }
    return ans;
}



#define MULTI_TEST_CASE false 
void solve(void){
    int f,n,k;
    cin >> f >> n >> k;
    long double ans = 0;
    for(int i = 1; i <= f; i++){
        for(int j = 0; j < k; j++){
            for(int l = k - j; l <= n - j; l++){
                //iより大きい目がj個、iがl個ある確率
                long double p = 1;
                int temp = j;
                while(temp--)p *= (long double)(f - i) / (long double)f;
                temp = l;
                while(temp--)p *= 1 / (long double)f;
                temp = n - j - l;
                while(temp--)p *= (long double)(i - 1) / (long double)f;
                //p *= binom(n,j) * binom(n - j,l)
                p *= binom(n,j);
                p *= binom(n - j,l);
                ans += p * i;
            }
        }
    }
    cout << fixed << setprecision(15);
    cout << ans << el;
    return;
}

void calc(void){
    return;
}

signed main(void){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    calc();
    int t = 1;
    if(MULTI_TEST_CASE)cin >> t;
    while(t--){
        solve();
    }
    return 0;
}