#include <bits/stdc++.h>

#define show(x) cerr << #x << " = " << x << endl

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "sz=" << v.size() << "\n[";
    for (const auto& p : v) {
        os << p << ",";
    }
    os << "]\n";
    return os;
}

template <typename S, typename T>
ostream& operator<<(ostream& os, const pair<S, T>& p)
{
    os << "(" << p.first << "," << p.second
       << ")";
    return os;
}


constexpr ll MOD = 1e9 + 7;

template <typename T>
constexpr T INF = numeric_limits<T>::max() / 100;

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll F, N, K;
    cin >> F >> N >> K;

    using ld = long double;
    ld sum = 0;
    for (ll i = 1; i <= F; i++) {
        for (ll k = 0; k < K; k++) {
            for (ll l = K - k; l <= N - k; l++) {
                ld prob = 1;
                for (ll j = 0; j < k; j++) {
                    prob *= (long double)(N - j) / (k - j);
                }
                for (ll j = 0; j < l; j++) {
                    prob *= (long double)(N - k - j) / (l - j);
                }
                prob *= pow(((long double)(i - 1) / F), N - k - l);
                prob *= pow(((long double)(F - i) / F), k);
                prob /= pow(F, l);
                sum += i * prob;
            }
        }
    }
    cout << fixed << setprecision(10) << sum << endl;

    return 0;
}