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

const int N = 305;
using db = long double;
const db eps = 1e-9;
int dcmp(const db &x)
{
    return abs(x) < eps ? 0 : (x < 0 ? -1 : 1);
}
db a[N][N];
db b[N];

void gauss(int n)
{
    for (int i = 0; i < n; i++)
    {
        int x = 0;
        for (int j = i; j < n; ++j)
            if (dcmp(a[j][i]) != 0)
            {
                x = j;
                break;
            }
        swap(b[x], b[i]);
        for (int j = 0; j < n; ++j)
            swap(a[x][j], a[i][j]);
        for (int j = i + 1; j < n; ++j)
        {
            db xi = a[j][i] / a[i][i];
            for (int k = i; k < n; k++)
            {
                a[j][k] -= xi * a[i][k];
            }
            b[j] -= xi * b[i];
        }
    }
    for (int i = n-1; i >= 0; --i)
    {
        b[i] /= a[i][i];
        a[i][i] = 1;
        for (int j = i - 1; j >= 0; --j)
        {
            db xi = a[j][i] / a[i][i];
            a[j][i] -= xi * a[i][i];
            b[j] -= xi * b[i];
        }
    }
}

void test_gauss()
{
    int n;
    cin >> n;
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= n; ++j)
            cin>>a[i][j];
        cin>>b[i];
    }
    gauss(n);
    for(int i=1;i<=n;++i){
        for(int j=1;j<=n;++j)
            cout<<a[i][j]<<" ";
        cout<<b[i]<<endl;
    }
}

int n, m;
db p;

int main()
{
    // test_gauss();
    cin >> n >> m >> p;cout << fixed << setprecision(12);
    for(int i=0;i<(1<<n);i++)
    {
        if((i&(1<<(n-1)))&&(__builtin_popcount(i)>=m))
        {
            a[i][i]=1;
            b[i]=0;
        }
        else 
        {
            a[i][i]=1;
            a[i][(i>>1)]-=(1-p);
            a[i][(i>>1)|(1<<(n-1))]-=p;
            b[i]=1;
        }
    }
    gauss(1<<n);
    db ans=0;
    
    cout << b[0] << "\n";
    return 0;
}