#include "bits/stdc++.h"
using namespace std;
#define all(x) begin(x), end(x)
#define sz(x) (int) (x).size()
#define int long long
#define ld long double

const int mxn = 505;
ld ft[mxn];

ld nck(int a, int b) {
	return ft[a]/ft[b]/ft[a-b];
}

array<ld,2> FF[mxn][mxn];

array<ld,2> f(int n, int d, int r) {
	if (FF[n][d][0]) return FF[n][d];
	//count, ev
//	cout<<n<<" "<<d<<" "<<r<<"\n";
	if (d < 0) {
		return {0,0};
	}
	if (n <= 0) {
		return {0,0};
	}
	if (!d) {
		return {1,0};
	}
	ld cnt = 0, val = 0;
	for (int rem=0; rem<=n; rem++) {
		auto [cc,vv] = f(n-rem,d-n+rem,r);
		if (!cc) continue;
		cnt += nck(n,rem) * cc;
		val += nck(n,rem) * (vv + min(n-rem,r)*cc);
//		if (d==3) {
//			cout<<n-rem<<" "<<d-n+rem<<": "<<nck(n,rem) * cc<<" "<<nck(n,rem) * (vv + min(n-rem,r))<<"\n";
//		}
	}
	
	FF[n][d] = {cnt,val};
	
	return {cnt,val};
}

signed main() {
	ios::sync_with_stdio(false); cin.tie(nullptr);
	
	ft[0] = 1;
	for (int i=1; i<mxn; i++) {
		ft[i] = i*ft[i-1];
	}
	
	int n,d,r; cin>>n>>d>>r;
	auto [a,b] = f(n,d,r);
	ld v = b/a+r;
	cout<<fixed<<setprecision(100)<<v;
	
	
}