#include <bits/stdc++.h>

#define rep(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;

const int MAXN = 20;
double dp[2][1<<MAXN];
int A[MAXN], B[MAXN];
double dpdp[2][MAXN][MAXN];

int main() {
    int N;
    double p[2];
    cin >> N >> p[0] >> p[1];
    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);
    dp[0][(1<<N)-1] = dp[1][(1<<N)-1] = 1;
    for (int j = 0; j < 2; j++) {
        for (int s = (1<<N)-2; s >= 1; s--) {
            bool first = true;
            int cnt = __builtin_popcount(s);
            for (int i = 0; i < N; i++) {
                if ((s>>i)&1) first = false;
                else {
                    if (first) dp[j][s] += dp[j][s|(1<<i)]*p[j];
                    else dp[j][s] += dp[j][s|(1<<i)]*(1-p[j])/cnt;
                }
            }
        }
    }
    for (int i = 0; i < N; i++) dp[0][0] += dp[0][(1<<i)];
    for (int j = 0; j < 2; j++) {
        for (int s = 1; s < (1<<N); s++) {
            int cnt = __builtin_popcount(s);
            bool first = true;
            for (int i = 0; i < 20; i++) {
                if ((s>>i)&1) {
                    if (cnt == 1) dpdp[j][N-cnt][i] += dp[j][s];
                    else {
                        if (first) {
                            first = false;
                            dpdp[j][N-cnt][i] += dp[j][s] * p[j];
                        } else {
                            dpdp[j][N-cnt][i] += dp[j][s] * (1-p[j])/(cnt-1);
                        }
                    }
                }
            }
        }
    }
    double ans = 0;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            for (int k = 0; k < N; k++) {
                if (A[j] > B[k]) {
                    ans += (A[j]+B[k]) * dpdp[0][i][j] * dpdp[1][i][k];
                }
            }
        }
    }
    printf("%.15lf\n", ans);
    return 0;
}