#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
ll mod=998244353;
ll inva(ll N) {
    ll a = N, b = mod, c = 1, d = 0;
    while (b > 0) {
        ll t = a / b;
        a -= t * b;
        swap(a, b);
        c -= t * d;
        swap(c, d);

    }
    c %= mod;
    if (c < 0)c += mod;
    return c;

}//割り算時に使う逆元を求める.


int main() {
    ll F,N,K;
    cin>>F>>N>>K;
    ll an=0;
    rep(i,5000000){
        vll A(N);
        rep(n,N){
            A[n]=1+rand()%F;
        }
        sort(all(A));
        an+=A[N-K];
    }
    cout<<setprecision(16)<<(an)/5000000.0<<endl;
}