#include <cstdio>
#include <algorithm>
using namespace std;

const int INF = 1 << 28;
int N; double p[2];
int cards[2][20];
double rec[2][20][25];
double dp[1 << 20];

void solve(int t) {
    fill(dp, dp + (1 << N), 0);
    dp[(1 << N) - 1] = 1.0;
    for(int bit=(1<<N)-1; bit>=0; bit--) {
        int mi = INF, idx = -1, cnt = 0;
        for(int i=0; i<N; i++) {
            if(bit >> i & 1) {
                cnt++;
                if(mi > cards[t][i]) {
                    mi = cards[t][i];
                    idx = i;
                }
            }
        }
        for(int i=0; i<N; i++) {
            if(bit >> i & 1) {
                int nbit = bit ^ (1 << i);
                int step = N - cnt + 1;
                if(cnt == 1) {
                    rec[t][i][step] += dp[bit];
                    dp[nbit] += dp[bit];
                }
                else {
                    double prob = (i == idx ? p[t] : (1 - p[t]) / (cnt - 1));
                    rec[t][i][step] += dp[bit] * prob;
                    dp[nbit] += dp[bit] * prob;
                }
            }
        }
    }
}

int main() {
    scanf("%d%lf%lf", &N, &p[0], &p[1]);
    for(int i=0; i<N; i++) {
        scanf("%d", &cards[0][i]);
    }
    for(int i=0; i<N; i++) {
        scanf("%d", &cards[1][i]);
    }
    solve(0); solve(1);

    double ans = 0.0;
    for(int step=1; step<=N; step++) {
        for(int x=0; x<N; x++) {
            for(int y=0; y<N; y++) {
                if(cards[0][x] < cards[1][y]) continue;
                ans += (cards[0][x] + cards[1][y]) * rec[0][x][step] * rec[1][y][step];
            }
        }
    }
    printf("%.12f\n", ans);
    return 0;
}