#include "bits/stdc++.h"
#define rep(i, a, n) for(auto i = a; i <= (n); i++)
#define per(i, a, n) for(auto i = n; i >= (a); i--)
#define pb push_back
#define mp make_pair
#define FI first
#define SE second
#define all(a) a.begin(), a.end()
#define sz(a) (int)(a).size()
template<class T> inline bool chmax(T &a, T b) { if(a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T &a, T b) { if(b < a) { a = b; return 1; } return 0; }
using namespace std;

template<class A, class B> string to_string(pair<A, B> p);
string to_string(const string &s) { return '"' + s + '"'; }
string to_string(const char *s) { return to_string((string) s); }
string to_string(char c) { return "'" + string(1, c) + "'"; }
string to_string(bool x) { return x ? "true" : "false"; }
template<class A> string to_string(A v)
{
    bool first = 1;
    string res = "{";
    for(const auto &x: v) 
    {
        if (!first) res += ", ";
        first = 0;
        res += to_string(x);
    }
    res += "}";
    return res;
}
template<class A, class B> string to_string(pair<A, B> p) { return "(" + to_string(p.FI) + ", " + to_string(p.SE) + ")"; }

void debug_out() { cerr << endl; }
template<class Head, class... Tail> void debug_out(Head H, Tail... T) 
{
    cerr << " " << to_string(H);
    debug_out(T...);
}
#ifndef ONLINE_JUDGE
    #define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
    #define debug(...) if(0) puts("No effect.")
#endif

using ll = long long;
// using LL = __int128;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using db = double;
using ldb = long double;

const int maxn = 200'000;
const int inf = 0x3f3f3f3f;
const int mod = 998244353;

template<class T> struct Matrix
{
    static constexpr T eps = static_cast<T>(1e-9);
    using Mat = Matrix;
    using vt = vector<T>;

    int n, m;
    vector<vt> a;
    Matrix(int n, int m): n(n), m(m), a(n, vt(m)) {}
    Matrix(const vector<vt> a): n(sz(a)), m(sz(a[0])), a(a) {}
    vt& operator [](int i) const { return (vt&)a[i]; }
    Mat inverse()
    {
        assert(n == m);
        auto b = a;

        rep(i, 0, n - 1) b[i].resize(n * 2, 0), b[i][n + i] = 1;
        rep(c, 0, n - 1)
        {
            int id = -1;
            rep(i, c, n - 1) if(abs(b[i][c]) > Mat::eps) { id = i; break; }
            assert(id != -1);
            if(id != c) swap(b[c], b[id]);
        
            T tmp = b[c][c];
            for(auto &x: b[c]) x /= tmp;
            rep(i, 0, n - 1) if(i != c)
            {
                T tmp = b[i][c];
                rep(j, 0, n * 2 - 1) b[i][j] -= tmp * b[c][j];
            }
        }
        for(auto &row: b) row.erase(row.begin(), row.begin() + n);
        return Mat(b);
    }
};

using Mat = Matrix<db>;

int main()
{
    ios::sync_with_stdio(0); cin.tie(0);

    int n, k; db p; cin >> n >> k >> p;
    int tot = 0;
    int N = 1 << n;
    vi id(N);
    rep(msk, 0, N - 1) if(__builtin_popcount(msk) >= k) id[msk] = -1; else id[msk] = tot++;
    
    Mat A(tot, tot);
    rep(i, 0, tot - 1) A[i][i] = 1;

    rep(msk, 0, N - 1) if(__builtin_popcount(msk) < k)
    {
        vector<db> P{1 - p, p};
        rep(i, 0, 1)
        {
            int nmsk = (msk >> 1) | (i << (n - 1));
            int x = id[msk];
            int y = id[nmsk];
            if(y != -1) A[x][y] -= P[i];
        }
    }
    auto iA = A.inverse();
    db ans = 0;
    for(auto x: iA[0]) ans += x;
    printf("%.10f\n", ans);
    return 0;
}