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

bool usedA[20];
bool usedB[20];

double perA[20][20];
double perB[20][20];

double dp[1 << 20];

int MAX = 1000;

int bitcount(int a){
	int ret = 0;
	while (a != 0){
		ret++;
		a = a & (a - 1);
	}
	return ret;
}

int main() {
	int N;
	double PA, PB;
	cin >> N >> PA >> PB;
	vector<int> A(N), B(N);
	for (int i = 0; i < N; i++)
	{
		cin >> A[i];
	}
	for (int i = 0; i < N; i++)
	{
		cin >> B[i];
	}
	sort(A.begin(), A.end());
	sort(B.begin(), B.end());

	
	for (int i = 0; i < (1<<N); i++)
	{
		dp[i] = 0;
	}
	dp[0] = 1;

	for (int i = 0; i < (1<<N); i++)
	{
		int count = bitcount(i);
		bool first = true;
		double firstp = 1;
		if (count != N - 1) firstp = PA;
		double secondp = 1 - firstp;
		if (count != N - 1) secondp /= (N - 1 - count);

		for (int j = 0; j < N; j++)
		{
			if ((i >> j) % 2 == 1) continue;
			double p = secondp;
			if (first){
				p = firstp;
				first = false;
			}
			dp[i + (1 << j)] += dp[i] * p;
			perA[count][j] += dp[i] * p;
		}
	}


	for (int i = 0; i < (1 << N); i++)
	{
		dp[i] = 0;
	}
	dp[0] = 1;
	
	for (int i = 0; i < (1 << N); i++)
	{
		int count = bitcount(i);
		bool first = true;
		double firstp = 1;
		if (count != N - 1) firstp = PB;
		double secondp = 1 - firstp;
		if (count != N - 1) secondp /= (N - 1 - count);

		for (int j = 0; j < N; j++)
		{
			if ((i >> j) % 2 == 1) continue;
			double p = secondp;
			if (first){
				p = firstp;
				first = false;
			}
			dp[i + (1 << j)] += dp[i] * p;
			perB[count][j] += dp[i] * p;
		}
	}


	double ans = 0;
	double sum = 0;
	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < N; j++)
		{
			int move = 0;
			if (A[i] > B[j]) move = A[i] + B[j];
			//else continue;
			for (int k = 0; k < N; k++)
			{
				ans += move * perA[k][i] * perB[k][j];
				sum += perA[k][i] * perB[k][j];
			}
		}
	}
	printf("%.14f\n", ans);
}