#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

vector<vector<double> > getTable(VI A, double p){
    int n = SZ(A);
    vector<double> prob(1<<n);
    vector<vector<double> > useP(n, vector<double>(n)); 
    prob[0] = 1.0;
    for(int b=0;b<(1<<n);b++){
        if(prob[b] == 0) continue;
        int minp = 1<<28;
        int minIndex = -1;
        int rem = 0;
        FOR(i,n){
            if(b & (1<<i)) continue;
            rem++;
            if(minp > A[i]) {
                minp = A[i];
                minIndex = i;
            }
        }
        if(rem == 1){
            prob[b | (1<<minIndex)] += prob[b];
            useP[n - rem][minIndex] += prob[b];
        }else{
            FOR(i,n){
                if(b & (1<<i)) continue;
                if(i == minIndex){
                    prob[b | (1<<i)] += prob[b] * p;
                    useP[n - rem][i] += prob[b] * p;
                }else {
                    prob[b | (1<<i)] += prob[b] * (1.0 - p) / (rem - 1);
                    useP[n - rem][i] += prob[b] * (1.0 - p) / (rem - 1);
                }
            }
        }
    }
    return useP;
}

int main()
{
    int N;
    double pa,pb;
    cin>>N>>pa>>pb;
    VI A(N); FOR(i,N) cin>>A[i];
    VI B(N); FOR(i,N) cin>>B[i];

    auto t1 = getTable(A, pa);
    auto t2 = getTable(B, pb);
    double ans = 0 ;

    FOR(t,N){
        FOR(i,N) FOR(j,N){
            if(A[i] > B[j]){
                ans += t1[t][i] * t2[t][j] * (A[i] + B[j]);
            }
        }
    }

    printf("%.10f\n", ans);
    
    return 0;
}