#include <iostream>
#include <cstdio>
#include <fstream>
#include <algorithm>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <limits.h>
#include <math.h>
#include <functional>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <float.h>
#include <random>

#define repeat(i,n) for (int i = 0; (i) < (n); ++ (i))
#define debug(x) cerr << #x << ": " << x << '\n'
#define debugArray(x,n) for(long long hoge = 0; (hoge) < (n); ++ (hoge)) cerr << #x << "[" << hoge << "]: " << x[hoge] << '\n'
#define debugArrayP(x,n) for(long long hoge = 0; (hoge) < (n); ++ (hoge)) cerr << #x << "[" << hoge << "]: " << x[hoge].first<< " " << x[hoge].second << '\n'

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> Pii;
typedef vector<int> vint;
typedef vector<ll> vll;
const ll INF = LLONG_MAX/10;
const ll MOD = 1e9+7;

int F,N,K;
double ans=0;

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin>>F>>N>>K;
  for(int x=1;x<=F;x++){
    double CC=1,C=1;
    repeat(i,N+1){
      C=1;
      repeat(j,N-i+1){
        int k=N-i-j;
        if(i<K&&K<=i+j)ans += (double)x*pow(double(F-x)/F,i)*pow(1./F,j)*pow((double)(x-1)/F,k)*CC*C;
        C *= (N-i-j);
        C /= (j+1);
      }
      //debug(CC);
      CC *= (N-i);
      CC /= (i+1);
    }
  }
  printf("%.10lf\n",ans);
  return 0;
}