#include <bits/stdc++.h>

#define SZ(x) (int)x.size() - 1
#define all(x) x.begin(), x.end()
#define F(i, a, b) for (int i = (a); i <= (b); i++)
#define DF(i, a, b) for (int i = (a); i >= (b); i--)

using namespace std;
typedef long long ll;
typedef unsigned long long ull;

template <typename T> inline void chkmax(T &x, T y) {x = max(x, y); }
template <typename T> inline void chkmin(T &x, T y) {x = min(x, y); }
template <typename T> inline void read(T &x) {
	x = 0; int f = 1; char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
	for (; isdigit(c); c = getchar()) x = x * 10 + c - '0';
	x *= f;
}
template <typename T> inline void write(T x) {
	T l = 0;
	ull y = 0;
	if (!x) { putchar(48); return; }
	if (x < 0) { x = -x; putchar('-'); }
	while (x) { y = y * 10 + x % 10; x /= 10; ++l; }
	while (l) { putchar(y % 10 + 48); y /= 10; --l; }
}
template <typename T> inline void writeln(T x) { write(x); puts(""); }
template <typename T> inline void writes(T x) { write(x); putchar(32); }

const int N = 510;
long double C[N][N], f[N][N], g[N][N];

signed main() {
	int n, d, r; read(n); read(d); read(r);
	C[0][0] = 1;
	F(i, 1, n) {
		C[i][0] = 1;
		F(j, 1, i)
			C[i][j] = C[i - 1][j] + C[i - 1][j - 1];
	}
	// F(i, 1, d){
	// 	F(j, 0, i) cout << C[i][j] << " "; cout << endl;
	// }
	// cout << C[3][2] << endl;
	// f[0][0] = 1;
	F(i, 1, n) {
		f[i][0] = 1;
		F(j, 1, d)
			F(k, 0, min(i, j)) {
				f[i][j] += C[i][k] * f[k][j - k];
				g[i][j] += C[i][k] * (g[k][j - k] + min(k, r) * f[k][j - k]);
			}
	}
	// cout << f[n][d] << " " << g[n][d] << endl;
	cout << fixed << setprecision(25) << (long double) g[n][d] / f[n][d] + r;
	return 0;
}