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

#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
using ld = long double;
int N;
ld PA, PB;
int A[22], B[22];
int main() {
    cin >> N >> PA >> PB;
    assert((1LL << N) * (1LL << N) <= 1e8);
    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);
    vector<vector<ld>> dp(1 << N, vector<ld>(1 << N));
    dp[0][0] = 0;
    rep(a, 0, 1 << N) rep(b, 0, 1 << N) for (int i = 0, t = -1; i < N; i++) for (int j = 0, s = -1; j < N; j++) {
        int ac = __builtin_popcount(a);
        int bc = __builtin_popcount(b);
        if (a >> i & 1 && b >> j & 1) {
            if (t == -1) t = i;
            if (s == -1) s = j;
            ld pa, pb;
            if (ac == 1) pa = 1;
            else {
                if (t == i) pa = PA;
                else pa = (1 - PA) / (ac - 1);
            }
            if (bc == 1) pb = 1;
            else {
                if (s == j) pb = PB;
                else pb = (1 - PB) / (bc - 1);
            }
            dp[a][b] += pa * pb * (dp[a ^ (1 << i)][b ^ (1 << j)] + (A[i] + B[j]) * (A[i] > B[j]));
        }
    }
    cout << fixed << setprecision(16) << dp[(1 << N) - 1][(1 << N) - 1] << endl;
}