#include <bits/stdc++.h>

using namespace std;

int main() {
  int N, A[20], B[20];
  double X, Y;

  cin >> N >> X >> Y;
  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< double > dp1(1 << N), dp2(1 << N);
  vector< vector< double > > dp3(N + 1, vector< double >(N)), dp4(N + 1, vector< double >(N));
  dp1.back() = dp2.back() = 1.0;


  for(int i = (1 << N) - 1; i > 0; i--) {
    vector< int > enable;
    for(int j = 0; j < N; j++) {
      if((i >> j) & 1) enable.emplace_back(j);
    }
    if(enable.size() == 1) {
      dp1[0] += dp1[i];
      dp2[0] += dp2[i];
      dp3[enable.size()][enable[0]] += dp1[i];
      dp4[enable.size()][enable[0]] += dp2[i];
    } else {
      dp1[i & ~(1 << enable[0])] += dp1[i] * X;
      dp2[i & ~(1 << enable[0])] += dp2[i] * Y;
      dp3[enable.size()][enable[0]] += dp1[i] * X;
      dp4[enable.size()][enable[0]] += dp2[i] * Y;
      double Z = 1.0 / ((int) enable.size() - 1);
      for(int j = 1; j < enable.size(); j++) {
        dp1[i & ~(1 << enable[j])] += dp1[i] * Z * (1.0 - X);
        dp2[i & ~(1 << enable[j])] += dp2[i] * Z * (1.0 - Y);
        dp3[enable.size()][enable[j]] += dp1[i] * Z * (1.0 - X);
        dp4[enable.size()][enable[j]] += dp2[i] * Z * (1.0 - Y);
      }
    }
  }

  double ret = 0.0;
  for(int i = 1; i <= N; i++) {
    for(int j = 0; j < N; j++) {
      for(int k = 0; k < N; k++) {
        if(A[j] > B[k]) ret += dp3[i][j] * dp4[i][k] * (A[j] + B[k]);
      }
    }
  }

  cout << fixed << setprecision(10) << ret << endl;
}