#include <bits/stdc++.h>

using namespace std;

#define sz(x) (int) x.size()
#define all(a) a.begin(), a.end()

const int MAXN = 55;

long long s[MAXN][MAXN];

int n, a, b;
int p[MAXN];
double dp[MAXN];
long long cnt[MAXN];

int loopsNum() {
    vector<bool> used(n, 0);
    int res = 0;
    for (int i = 0; i < n; i++) {
        if (used[i]) continue;
        res++;
        int pos = i;
        while (!used[pos]) {
            used[pos] = true;
            pos = p[pos];
        }
    }
    return res;
}

int main() {

    scanf("%d %d %d", &n, &a, &b);
    for (int i = 0; i < n; i++) {
        scanf("%d", &p[i]);
        p[i]--;
    }

    s[0][0] = 1;
    for (int i = 0; i < n; i++) {
        for (int j = 1; j <= n; j++) {
            s[i + 1][j] = 1ll * i * s[i][j] + s[i][j - 1];
        }
    }
    // for (int i = 0; i <= n; i++) {
    //     for (int j = 0; j <= i; j++) {
    //         cerr << s[i][j] << " ";
    //     }
    //     cerr << endl;
    // }

    long long total = 1;
    // cerr << "CNT" << endl;
    for (int i = 1; i <= n; i++) {
        cnt[i] = s[n][i];
        total = 1ll * total * i;
        // cerr << cnt[i] << " ";
    }
    // cerr << endl << total << endl;

    // cerr << "LOOPS: " << loopsNum() << endl;
    int loops = loopsNum();

    double ans = 1.0 * a * (n - loops);

    for (int i = n; i >= 1; i--) {
        for (int j = n; j >= 1; j--)
            dp[j] = 0.0;
        for (int j = n; j >= 1; j--) {
            if (j >= i) {
                dp[j] = 1.0 * a * (n - j);
            } else {
                dp[j] = 1.0 * b;
                // cerr << "HERE1 " << dp[j] << endl;
                for (int k = n; k >= i; k--)
                    dp[j] += 1.0 * dp[k] * cnt[k] / total;
                // cerr << "HERE2 " << dp[j] << endl;
                long long sum = 0;
                for (int k = i - 1; k >= 1; k--)
                    sum += cnt[k];
                // cerr << "HERE3 " << dp[j] << endl;
                dp[j] = 1.0 * dp[j] * total / (total - sum);
            }
            // cerr << dp[j] << " ";
        }
        // cerr << endl;
        ans = min(ans, dp[loops]);
    }

    printf("%.12lf\n", ans);

    return 0;
}