#include <bits/stdc++.h>

#define db double

const db eps = 1e-6 ;
const int MAX_N = 100 + 10 ;

int n , m , k ;
db p , A[MAX_N][MAX_N] ;
bool ed[MAX_N] , sam[MAX_N] ;

void gauss() {
    for (int i = 0 ; i < m ; ++i) {
        for (int j = i + 1 ; j < m ; ++j)
            if (abs(A[i][i]) < abs(A[j][i])) for (int k = 0 ; k <= m ; ++k) std::swap(A[i][k] , A[j][k]) ;

        for (int j = i + 1 ; j < m ; ++j) {
            db xs = A[j][i] / A[i][i] ;
            for (int k = i ; k <= m ; ++k) A[j][k] -= xs * A[i][k] ;
        }
    }

    for (int i = m - 1 ; i >= 0 ; --i) {
        for (int j = i + 1 ; j < m ; ++j) A[i][m] -= A[j][m] * A[i][j] ;
        if (abs(A[i][i]) > eps) A[i][m] /= A[i][i] ;
        else A[i][m] = 0 ;
    }
}

int main() {
    scanf("%d %d %lf" , &n , &k , &p) ;

    m = (1 << n) ;
    for (int i = 0 ; i < m ; ++i) {
        int cnt = 0 ;
        for (int j = 0 ; j < n ; ++j) if ((1 << j) & i) ++cnt ;

        if (cnt >= k) ed[i] = 1 ;
        else if (cnt == k) sam[i] = 1 ;
    }

    for (int i = 0 ; i < m ; ++i) {
        A[i][i] = 1 ;
        if (sam[i]) A[i][m] = 1 ;
        if (ed[i]) continue ;

        for (int j = 0 ; j < 2 ; ++j) {
            int ni = (i << 1) & (m - 1) | j ;

            A[i][m] = 1 ;
            if (j) A[i][ni] -= p ;
            else A[i][ni] -= 1 - p ;
        }
    }
    gauss() ;
    printf("%0.7lf\n" , A[0][m]) ;

    return 0 ;
}