#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>

using namespace std;
typedef long long ll;

const int MAXN = 22;
int N;
double pa, pb;
int A[MAXN], B[MAXN];
double dpa[MAXN][MAXN], dpb[MAXN][MAXN];

void dfsa(int cur, int s, double p) {
    if (cur == N-1) {
        for (int i = 0; i < N; i++) {
            if ((s>>i)&1) {
                dpa[i][cur] += p;
                break;
            }
        }
        return;
    }
    bool first = false;
    int cnt = __builtin_popcount(s);
    for (int i = 0; i < N; i++) {
        if ((s>>i)&1) {
            if (!first) {
                dpa[i][cur] += p*pa;
                first = true;
                dfsa(cur+1, s^(1<<i), p*pa);
            } else {
                dpa[i][cur] += p*(1-pa)/(cnt-1);
                dfsa(cur+1, s^(1<<i), p*(1-pa)/(cnt-1));
            }
        }
    }
}

void dfsb(int cur, int s, double p) {
    if (cur == N-1) {
        for (int i = 0; i < N; i++) {
            if ((s>>i)&1) {
                dpb[i][cur] += p;
                break;
            }
        }
        return;
    }
    bool first = false;
    int cnt = __builtin_popcount(s);
    for (int i = 0; i < N; i++) {
        if ((s>>i)&1) {
            if (!first) {
                dpb[i][cur] += p*pb;
                first = true;
                dfsb(cur+1, s^(1<<i), p*pb);
            } else {
                dpb[i][cur] += p*(1-pb)/(cnt-1);
                dfsb(cur+1, s^(1<<i), p*(1-pb)/(cnt-1));
            }
        }
    }
}

int main(void) {
    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);
    dfsa(0, (1<<N)-1, 1);
    dfsb(0, (1<<N)-1, 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 += dpa[j][i] * dpb[k][i] * (A[j]+B[k]);
            }
        }
    }
    printf("%.10lf\n", ans);
    return 0;
}