#include<bits/stdc++.h>
#if __has_include(<atcoder/all>)
#endif
using namespace std;
#define LL(...) ll __VA_ARGS__;lin(__VA_ARGS__)
#define fo(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define fe(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):a)
#define defpp template<ostream&o=cout>void pp(const auto&...a){[[maybe_unused]]const char*c="";((o<<c<<a,c=" "),...);o<<'\n';}void epp(const auto&...a){pp<cerr>(a...);}
#define entry defpp void main();void main2();}int main(){my::io();my::main();}namespace my{
namespace my{
void io(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);}
using dd=double;
using ll=long long;
template<class T>concept modulary=requires(T t){t.mod();};
template<class T>constexpr auto for_range(T s,T b){T a=0;if(s)swap(a,b);return array{a-s,b,1-s*2};}
template<class T>constexpr auto for_range(T s,T a,T b,T c=1){return array{a-s,b,(1-s*2)*c};}
void lin(auto&...a){(cin>>...>>a);}
constexpr auto pow(auto x,ll n,auto e){assert(n>=0);decltype(x)r=e;for(;n;x*=x,n>>=1)if(n&1)r*=x;return r;}
constexpr auto pow(auto x,ll n){return pow(x,n,1);}
template<class...A>using pack_back_t=tuple_element_t<sizeof...(A)-1,tuple<A...>>;
}
namespace my{
template<class V>concept vectorial=is_base_of_v<vector<typename remove_cvref_t<V>::value_type>,remove_cvref_t<V>>;
template<class V>struct vec;
template<int D,class T>struct hvec_helper{using type=vec<typename hvec_helper<D-1,T>::type>;};
template<class T>struct hvec_helper<0,T>{using type=T;};
template<int D,class T>using hvec=hvec_helper<D,T>::type;
template<class V>struct vec:vector<V>{
  using vector<V>::vector;
  ll size()const{return vector<V>::size();}
  vec rev_mobius()const{vec v=*this;if constexpr(vectorial<V>){ }fo(i,v.size()-1)v[i]-=v[i+1];return v;}
};
template<class...A>requires(sizeof...(A)>=2)vec(const A&...a)->vec<hvec<sizeof...(A)-2,pack_back_t<A...>>>;
}
namespace my{
template<class T>T fac(ll n){static vec<T>v{1};if(ll m=v.size();m<=n){v.resize(n+1);fo(i,m,n+1)v[i]=v[i-1]*i;}return v[n];}
template<class T>T comb(ll n,ll k){
  if(n<0||k<0||n<k)return 0;
  if constexpr(modulary<T>){ }
  else return fac<T>(n)/fac<T>(k)/fac<T>(n-k);
}
}
namespace my{entry
void main(){
  LL(F,N,K);

  // K番目の値を表す確率変数をXとすると,
  // E[X]=\sum_{x=1}^F p(x)*x (p(x):大きい方からK番目がxの確率)
  // E[X]=\sum_{x=1}^F q(x) (q(x):大きい方からK番目がx以上の確率=x以上がK回以上出る確率)
  vec<dd>q(F+1);
  fo(x,1,F+1){
    dd P=dd(F-(x-1))/F;
    dd Q=dd(x-1)/F;
    fo(k,K,N+1)q[x]+=pow(P,k)*pow(Q,N-k)*comb<dd>(N,k);
  }

  auto p=q.rev_mobius();
  dd ans=0;
  fo(x,1,F+1)ans+=p[x]*x;
  pp(ans);
}}