#include <bits/stdc++.h>
using namespace std;

// #define int long long
#define rep(i, n) for (long long i = (long long)(0); i < (long long)(n); ++i)
#define reps(i, n) for (long long i = (long long)(1); i <= (long long)(n); ++i)
#define rrep(i, n) for (long long i = ((long long)(n)-1); i >= 0; i--)
#define rreps(i, n) for (long long i = ((long long)(n)); i > 0; i--)
#define irep(i, m, n) for (long long i = (long long)(m); i < (long long)(n); ++i)
#define ireps(i, m, n) for (long long i = (long long)(m); i <= (long long)(n); ++i)
#define irreps(i, m, n) for (long long i = ((long long)(n)-1); i > (long long)(m); ++i)
#define SORT(v, n) sort(v, v + n);
#define REVERSE(v, n) reverse(v, v+n);
#define vsort(v) sort(v.begin(), v.end());
#define all(v) v.begin(), v.end()
#define mp(n, m) make_pair(n, m);
#define cinline(n) getline(cin,n);
#define replace_all(s, b, a) replace(s.begin(),s.end(), b, a);
#define PI (acos(-1))
#define FILL(v, n, x) fill(v, v + n, x);
#define sz(x) (long long)(x.size())

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vs = vector<string>;
using vpll = vector<pair<ll, ll>>;
using vtp = vector<tuple<ll,ll,ll>>;
using vb = vector<bool>;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<class t> using vc=vector<t>;
template<class t> using vvc=vc<vc<t>>;

const ll INF = 1e9+10;
const ll MOD = 1e9+7;
const ll LINF = 1e18;

// n引いて、あるxが上からk番目の値となる
// 自分以上の値から(k-1)個、自分1個、自分以下(n-k)個
// これだと同じ場合の確率を重複してカウントしてしまう？
// 自分未満、自分、自分より大きい、に分別
// 今xをk番目にしたい
// xより大(f-x)がa個なら、xはk-a個以上必要、xがb個なら、x未満(x-1)は、n-a-b個
// ↑の中でも同じ集合だが、順列としては別として数えられる場合もある
// n!/(a!*b!*c!)


signed main()
{
  cin.tie( 0 ); ios::sync_with_stdio( false );
  
  ll f,n,k; cin>>f>>n>>k;
  
  vc<double> fact(105);
  fact[0]=1.0;
  rep(i,100) fact[i+1]=fact[i]*(i+1);
  
  double ans=0;
  reps(i,f){
    double up=(f-i)*1.0/f, down=(i-1)*1.0/f, pre=1.0/f;
    double p=0;
    rep(a,k){
      irep(b,k-a,n-a+1){
        ll c=n-a-b;
        double x=pow(up,a)*pow(pre,b)*pow(down,c)*(fact[n]/(fact[a]*fact[b]*fact[c]));
        // printf("%d %d %d %d %.15lf\n", i,a,b,c,x);
        p+=x;
      }
    }
    ans+=p*i;
  }
  printf("%.15lf\n", ans);
}