#include <iostream> #include <cstdio> #include <fstream> #include <algorithm> #include <string> #include <map> #include <set> #include <queue> #include <stack> #include <vector> #include <limits.h> #include <math.h> #include <functional> #include <bitset> #include <iomanip> #include <cassert> #include <float.h> #include <random> #define repeat(i,n) for (int i = 0; (i) < (n); ++ (i)) #define debug(x) cerr << #x << ": " << x << '\n' #define debugArray(x,n) for(long long hoge = 0; (hoge) < (n); ++ (hoge)) cerr << #x << "[" << hoge << "]: " << x[hoge] << '\n' #define debugArrayP(x,n) for(long long hoge = 0; (hoge) < (n); ++ (hoge)) cerr << #x << "[" << hoge << "]: " << x[hoge].first<< " " << x[hoge].second << '\n' using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair<int,int> Pii; typedef vector<int> vint; typedef vector<ll> vll; const ll INF = LLONG_MAX/10; const ll MOD = 1e9+7; int N; double P[2]; double dp[2][(1<<20)+10]; double dp2[2][30][30]; int card[2][30]; int main(){ cin.tie(0); ios::sync_with_stdio(false); cin>>N; cin>>P[0]>>P[1]; repeat(c,2)repeat(i,N)cin>>card[c][i]; repeat(c,2)sort(card[c],card[c]+N); //debugArray(card[0],N); //debugArray(card[1],N); dp[0][(1<<N)-1] =dp[1][(1<<N)-1]= 1; repeat(c,2){ for(int b=(1<<N)-2;b>0;b--){ int cnt=__builtin_popcount(b); int minb = __builtin_ffs(b)-1; repeat(i,N)if(!((b>>i)&1)){ dp[c][b] += ((i<minb)? P[c]:(1.0-P[c])/cnt)*dp[c][b|(1<<i)]; } } } //debugArray(dp[0],((1<<N))); repeat(c,2){ for(int b=(1<<N)-1;b>0;b--){ int t=N-__builtin_popcount(b); int minb = __builtin_ffs(b)-1; repeat(i,N)if((b>>i)&1){ dp2[c][t][i] += (t==N-1? 1:(i==minb)? P[c]:(1.0-P[c])/(N-t-1))*dp[c][b]; } } } double ans = 0; repeat(t,N){ repeat(a,N){ repeat(b,N){ if(card[0][a] > card[1][b]){ ans += dp2[0][t][a]*dp2[1][t][b]*(card[0][a]+card[1][b]); } } } } printf("%.10lf\n",ans); return 0; }