#include <bits/stdc++.h>
using namespace std;
#define rng(i, a, b) for(int i=(int)a;i<(int)b;i++)
#define rep(i,n) rng(i,0,n)
using ld=long double;
const ld eps=1e-9;
bool is0(ld x){ return -eps<=x&&x<=eps; }
template<class t>using vc=vector<t>;
template<class t>using vvc=vc<vc<t>>;
#define a first
#define b second
using vi=vc<int>;
#define pb push_back
#define eb emplace_back
#define pcnt(x) __builtin_popcount(x)
template<class t,class u>bool chmax(t &a,u b){
	if(a <b){a=b;return true;}
	else return false;
}
vi sweep(vvc<ld>&a, int c=-1){
	if(a.empty()) return {};
	if(c==-1)c=a[0].size();
	int h=a.size(),w=a[0].size(),r=0;
	vi res;
	rep(i,c){
		if(r==h)break;
		pair<ld,int>mx(0,-1);
		rng(j,r,h)chmax(mx,make_pair(abs(a[j][i]),j));
		if(is0(mx.a)) continue;
		swap(a[r],a[mx.b]);
		rep(j,h) if(j!=r){
			ld z=-a[j][i]/a[r][i];
			rng(k,i,w)a[j][k]+=a[r][k]*z;
		}
		res.pb(i);
		r++;
	}
	return res;
}
vvc<ld> inverse(vvc<ld>a){
	int n=a.size();
	rep(i,n){
			a[i].resize(2*n);
			a[i][n+i]=1;
	}
	auto tmp=sweep(a,n);
	assert((int)tmp.size()==n);
	vvc<ld>b(n,vc<ld>(n));
	rep(i,n)rep(j,n)b[i][j]=a[i][n+j]/a[i][i];
	return b;
}
void slv(){
	int n,k; cin >> n >> k;
	ld p; cin >> p;
	vc<int>A;
	rep(i, (1<<n)) if(pcnt(i) < k) A.pb(i);
	int sz = A.size();
	vvc<ld>t(sz,vc<ld>(sz));
	vc<ld>vec(sz);
	rep(i, sz){
		int num = A[i];
		{
			t[i][i] = 1.0L;
			int v = (num<<1)%(1<<n);
			t[i][lower_bound(A.begin(), A.end(), v) - A.begin()] -= 1.0-p;
			v++;
			if(pcnt(v) < k) t[i][lower_bound(A.begin(), A.end(), v) - A.begin()] -= p;
			vec[i]=1.0;
		}
	}
	auto rt = inverse(t);
	ld ans=0;
	rep(i,sz) ans+=rt[0][i] * vec[i];
	cout<<ans<<'\n';
}
signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(20);
	slv();
}