#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;

#define FOR(i, a, b) for (int i = a; i < (b); i++)
#define F0R(i, a) for (int i = 0; i < (a); i++)
#define FORd(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define F0Rd(i, a) for (int i = (a) - 1; i >= 0; i--)
#define trav(a, x) for (auto &a : x)
#define sz(x) (int)(x).size()
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define ins insert

const char nl = '\n';

ld dp[501][501][501];

void solve() {
	ld logs[1001];
	FOR(i, 1, 1001) {
		logs[i] = log(i);
	}
	ld logFac[1001];
	logFac[0] =0 ;
	FOR(i, 1, 1001) {
		logFac[i] = logFac[i-1] + logs[i];
	}
	F0R(i, 501) F0R(j, 501) F0R(k, 501) dp[i][j][k] = -1000;
	int N, D, R; cin >> N >> D >> R;
	dp[0][D][D] = 0;
	ld ans = -1000;
	F0R(i, N+1) {
		F0Rd(j, D+1) {
			F0Rd(k, D+1) {
				//cout << i << " " << j << " " << k << ": " << dp[i][j][k] << " " << exp(dp[i][j][k]) << nl;
				if (dp[i][j][k] < -999) {
					continue;
				}
				if ((N-i) * k < j) continue;
				if (k == 0) {
					if (j == 0) {
						ld cur = dp[i][j][k];
						if (i < R) cur += logs[D];
						ans = log(exp(ans) + exp(cur));
					}
					continue;
				}
				ld nv = dp[i][j][k];
				if (k) {
					dp[i][j][k-1] = log(exp(dp[i][j][k-1]) + exp(dp[i][j][k]));
				}
				for (int nxt = 1; nxt * k <= j && nxt + i <= N; nxt++) {
					nv += logs[N-i-nxt+1]; nv -= logs[nxt];
					nv += logFac[j-(nxt-1)*k]; nv -= logFac[j-nxt*k];
					if (i+nxt == R) {
						nv += logs[D-(j-nxt*k)];
					}
					//cout << i << " " << j << " " << k << " " << nxt << " " << exp(nv) << nl;
					dp[i+nxt][j-nxt*k][k-1] = log(exp(dp[i+nxt][j-nxt*k][k-1]) + exp(nv));
				}
			}
		}
	}
	FOR(i, N, N+D) {
		ans -= logs[i];
	}
	cout << fixed << setprecision(15) << exp(ans) + R << nl;

}

int main() {
	ios_base::sync_with_stdio(0); cin.tie(0);
	solve();
	return 0;
}