#include<iostream>
#include<cstdio>
#define N 1000
using namespace std;
int read()
{
	char c=0;
	int sum=0;
	while (c<'0'||c>'9') c=getchar();
	while ('0'<=c&&c<='9') sum=sum*10+c-'0',c=getchar();
	return sum;
}
int n,d,r;
double ans,C[N+1][N+1],dp[N+1][N+1][2];
int main()
{
	int cnt;
	double res;
	for (int i=0;i<=N;++i) C[i][0]=1;
	for (int i=1;i<=N;++i)
		for (int j=1;j<=i;++j)
			C[i][j]=C[i-1][j-1]+C[i-1][j];
	n=read(),d=read(),r=read(),dp[0][0][0]=1;
	for (int i=d;i>=1;--i)
		for (int j=n;j>=1;--j)
			for (int t=0;t<=d;++t)
			{
				res=1;
				for (int k=1;k<=min(j,t/i);++k)
				{
					cnt=max(min(r-(j-k),k),0)*i,res*=C[t-(k-1)*i][i]/C[n+t-(k-1)*i-1][i];
					dp[j][t][0]+=dp[j-k][t-i*k][0]*res*C[j][k];
					dp[j][t][1]+=dp[j-k][t-i*k][0]*res*C[j][k]*cnt;
					dp[j][t][1]+=dp[j-k][t-i*k][1]*res*C[j][k];
				}
			}
	ans=r;
	for (int i=0;i<=n;++i) ans+=dp[i][d][1]*C[n][i];
	printf("%0.12lf\n",ans);
	return 0;
}