#include<algorithm>
#include<cstdio>
typedef double real;
const int maxn=500,maxd=500;
int n,d,r;
real C[maxn+1][maxn+1],f[maxd+1][maxn+1],g[maxd+1][maxn+1],F,G;
int main(){
	scanf("%d%d%d",&n,&d,&r);
	for(int i=0;i<=n;i++){
		C[i][0]=1;
		for(int j=1;j<=n;j++)C[i][j]=C[i-1][j-1]+C[i-1][j];
	}
	f[0][n]=1,g[0][n]=r;
	for(int S=0;S<d;S++)
		for(int i=1;i<=n;i++)
			for(int _i=1;_i<=i&&S+_i<=d;_i++){
				f[S+_i][_i]+=f[S][i]*C[i][_i];
				g[S+_i][_i]+=(g[S][i]+f[S][i]*std::min(_i,r))*C[i][_i];
			}
	for(int i=1;i<=n;i++)F+=f[d][i],G+=g[d][i];
	printf("%.9lf\n",G/F);
	return 0;
}