#include <bits/stdc++.h>
using namespace std;

typedef long double frac;

const frac eps=1e-6;

namespace gauss{
	
	frac a[533][533],ans[533];
	void gauss(int ROW,int COLUMN){
		int m=COLUMN,r=1;
		int n=ROW;
		for (int i=1;i<=m && r<=n;i++){
			frac maxx=0;
			int maxp=r;
			for (int j=r;j<=n;j++){
				if (abs(a[j][i])>abs(maxx)){
					maxx=a[j][i],maxp=j;
					break;	
				}
			}
			if (abs(maxx)<eps) continue;
			for (int j=i;j<=m;j++)
				swap(a[r][j],a[maxp][j]);
			for (int j=r+1;j<=n;j++){
				frac t=a[j][i]/a[r][i];
				for (int k=i;k<=m;k++){
					a[j][k]=a[j][k]-t*a[r][k];
				}
			}
			r++;
		}
		for (int i=n;i>=1;i--){
			for (int j=1;j<=m;j++){
				if (abs(a[i][j])>eps){
					frac t=a[i][j];
					for (int l=j;l<=m;l++) a[i][l]=a[i][l]/t;
					for (int k=i-1;k>=1;k--){
						frac t=a[k][j]/a[i][j];
						for (int l=j;l<=m;l++)
							a[k][l]=a[k][l]-t*a[j][l];
					}
					break;
				}
			}
		}
		
	}
}

int n,k;
frac p;

int main(){
	ios_base::sync_with_stdio(false);
	cin >> n >> k >> p;
	
	int mx=(1<<n)-1;
	for (int mask=0;mask<=mx;mask++){
		int nxt0=((mask<<1)&mx)|0;
		int nxt1=((mask<<1)&mx)|1;
		gauss::a[mask+1][mask+1]+=1.0;
		if (__builtin_popcount(mask)>=k){
			gauss::a[mask+1][mx+2]=0.0;
		}
		else{
			gauss::a[mask+1][nxt0+1]-=(1-p);
			gauss::a[mask+1][nxt1+1]-=p;
			gauss::a[mask+1][mx+2]+=1.0;
		}
	}
	
	gauss::gauss(mx+1,mx+2);
	cout << fixed << setprecision(12) << gauss::a[1][mx+2] << "\n";
	
	return 0;
}