#include <limits>
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = uint32_t;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int f, n, k;
    cin >> f >> n >> k;
    k = n-k+1;
    double ans = 0;
    vector<double> logfact(n+1);
    for (int i = 0; i < n; ++i) {
        logfact[i+1] = logfact[i] + log(i+1);
    }
    auto F = [&](double i, double j) {
        if(j == 0) return 0.0;
        if(j == f) return 1.0;
        return exp(logfact[n]-logfact[i]-logfact[n-i] + i * log(1.0*j/f) + (n-i) * log(1.0 * (f-j)/f));
    };
    vector<double> dp(f+1, 1);
    for (int j = 0; j < f; ++j) {
        double a = 0;
        for (int i = k; i <= n; ++i) {
            a += F(i, j);
        }
        dp[j] = a;
    }
    for (int j = 0; j < f; ++j) {
        ans += (dp[j+1]-dp[j])*(j+1);
    }
    printf("%.10lf\n", ans);
    return 0;
}