#include <iostream>
#include <iomanip>
#include <cmath>
#include <vector>

template <class T>
struct Combination {
    int max_n;
    std::vector<T> f, invf;

    explicit Combination(int n)
        : max_n(n), f(n + 1), invf(n + 1) {
        f[0] = 1;
        for (int i = 1; i <= n; ++i) {
            f[i] = f[i - 1] * i;
        }

        invf[max_n] = T(1) / f[max_n];
        for (int i = max_n - 1; i >= 0; --i) {
            invf[i] = invf[i + 1] * (i + 1);
        }
    }

    T fact(int n) const { return n < 0 ? T(0) : f[n]; }
    T invfact(int n) const { return n < 0 ? T(0) : invf[n]; }
    T perm(int a, int b) const {
        return a < b || b < 0 ? T(0) : f[a] * invf[a - b];
    }
    T binom(int a, int b) const {
        return a < b || b < 0 ? T(0) : f[a] * invf[a - b] * invf[b];
    }
};

using ldouble = long double;
const Combination<ldouble> C(100);

void solve() {
    int f, n, k;
    std::cin >> f >> n >> k;

    ldouble ans = 0;
    for (int m = 1; m <= f; ++m) {
        ldouble p = ldouble(m) / f;
        ldouble prob = 1;
        for (int i = 0; i < k; ++i) {
            prob -= C.binom(n, i) * std::pow(p, i) * std::pow(1 - p, n - i);
        }
        ans += prob;
    }

    std::cout << ans << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(10);

    solve();

    return 0;
}