#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a,b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define spair(p) cout<<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout<<" "<<kbrni;cout<<endl
#define smap(m) cout<<#m<<":";each(kbrni,m)cout<<" {"<<kbrni.first<<":"<<kbrni.second<<"}";cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 105;

double comb[MAX_N][MAX_N];

void make(int N){
    rep(i,N+1){
        comb[i][0] = 1;
    }
    for(int i=1;i<=N;i++){
        for(int j=1;j<=i;j++){
            comb[i][j] = comb[i-1][j] + comb[i-1][j-1];
        }
    }
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int F,N,K;
    cin >> F >> N >> K;
    make(N);
    double ans = 0;
    for(int i=1;i<=F;i++){
        double val = 0;
        for(int j=1;j<=N;j++){
            for(int k=max(K-j,0);k<=min(K-1,N-j);k++){
                val += pow(i-1,k)*pow(F-i,N-j-k)*comb[N][j+k]*comb[j+k][j]/pow(F,N);
            }
        }
        ans += (F+1-i)*val;
    }
    printf("%.12lf\n",ans);
    return 0;
}