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

#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
using ld = double;
int main() {
    int N;
    ld PA, PB;
    int A[22], B[22];
    cin >> N >> PA >> PB;
    for (int i = 0; i < N; i++) cin >> A[i];
    for (int i = 0; i < N; i++) cin >> B[i];
    sort(A, A + N), sort(B, B + N);
    auto pos = [&](int b, int i, ld P) -> ld {
        assert(b >> i & 1);
        int bc = __builtin_popcount(b);
        if (bc == 1) return 1.;
        else {
            int bit = 1 << i;
            int s = b & (-b);
            if (bit == s) return P;
            else return (1 - P) / (bc - 1);
        }
    };
    auto calc = [&](ld P) {
        vector dp(N + 1, vector<ld>(1 << N));
        dp[0][(1 << N) - 1] = 1;
        for (int r = 0; r < N; r++) {
            for (int b = 0; b < (1 << N); b++) {
                for (int i = 0; i < N; i++) {
                    if (b >> i & 1) {
                        int nb = b ^ (1 << i);
                        dp[r + 1][nb] += dp[r][b] * pos(b, i, P);
                    }
                }
            }
        }
        return dp;
    };
    auto dpa = calc(PA);
    auto dpb = calc(PB);
    auto f = [&](int i, int r, const vector<vector<ld>>& dp, ld P) {
        ld t = 0;
        for (int b = 0; b < (1 << N); b++) {
            if (b >> i & 1) t += dp[r][b] * pos(b, i, P);
        }
        return t;
    };
    ld ans = 0;
    for (int r = 1; r <= N; r++) {
        vector<ld> p(N), q(N);
        for (int i = 0; i < N; i++) p[i] = f(i, r - 1, dpa, PA);
        for (int j = 0; j < N; j++) q[j] = f(j, r - 1, dpb, PB);
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < N; j++) {
                ans += p[i] * q[j] * ((A[i] + B[j]) * (A[i] > B[j]));
            }
        }
    }
    cout << fixed << setprecision(17) << ans << endl;
}