#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1010;
int f,n,k;
double ans;
signed main(){
	//freopen("dice.in","r",stdin);
	//freopen("dice.out","w",stdout);
	cin>>f>>n>>k;
	for(int x=1;x<=f;x++){
		double p1=1.0*(f-x)/f,p2=1.0/f;
		double p3=1.0-p1-p2;
		double s=0.0;
		for(int i=0;i<k;i++){
			for(int j=k-i;j<=n-i;j++){
				int t=n-i-j;
				double p=1.0;
				for(int l=1;l<=i;l++)p*=p1;
				for(int l=1;l<=j;l++)p*=p2;
				for(int l=1;l<=t;l++)p*=p3;
				for(int l=1;l<=n;l++)p*=l;
				for(int l=1;l<=i;l++)p/=l;
				for(int l=1;l<=j;l++)p/=l;
				for(int l=1;l<=t;l++)p/=l;
				s+=p;
			}
		}
		ans+=s*x;
	}
	cout<<fixed<<setprecision(15)<<ans<<'\n';
	return 0;
}