#include <cstdio>
#include <cassert>
#include <cmath>
#include <cstring>

#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <functional>
#include <stack>
#include <queue>

#include <tuple>

#define getchar getchar_unlocked
#define putchar putchar_unlocked

#define _rep(_1, _2, _3, _4, name, ...) name
#define rep2(i, n) rep3(i, 0, n)
#define rep3(i, a, b) rep4(i, a, b, 1)
#define rep4(i, a, b, c) for (int i = int(a); i < int(b); i += int(c))
#define rep(...) _rep(__VA_ARGS__, rep4, rep3, rep2, _)(__VA_ARGS__)

using namespace std;

using i64 = long long;
using u8 = unsigned char;
using u32 = unsigned;
using u64 = unsigned long long;
using f80 = long double;

void solve() {
  const int F_MAX = 20, N_MAX = 100;
  int F, N, K;
  while (~scanf("%d %d %d", &F, &N, &K)) {
    vector<double> facts(N + 1, 1.0);
    rep(i, 1, N + 1) facts[i] = facts[i - 1] * i;
    double ans = 0.0;
    rep(j, 1, F) {
      double p = 1.0, q = pow(F - j, N);
      rep(i, K) ans += p / facts[i] * q / facts[N - i], p *= j, q /= F - j;
    }
    printf("%.15f\n", F - ans / pow(F, N) * facts[N]);
  }
}

int main() {
  clock_t beg = clock();
  solve();
  clock_t end = clock();
  fprintf(stderr, "%.3f sec\n", double(end - beg) / CLOCKS_PER_SEC);
  return 0;
}