#pragma comment(linker, "/STACK:65777216")
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <stack>
#include <map>
#include <queue>
#include <string>
#include <memory.h>
#include <iterator>
#define y1 trololoy1
#define y0 trololoy0
#define mem(A,X) memset(A,X,sizeof(A))
#define memo(A) memset(A,0,sizeof(A))
#define forn(I,B) for (int I=1;I<=(B);I++)
#define forg(H,V) for (int H=first[V];h;h=next[H])
#define rep(I,B) for (int I=0;I<(B);I++)
#define labs(X) (((X)>0)?(X):(-(X)))
#define ropen(X) freopen(X,"r",stdin)
#define wopen(X) freopen(X,"w",stdout)
#define rwopen(X) freopen(X".in","r",stdin);freopen(X".out","w",stdout)
#define pb push_back
#define mp make_pair
#define all(X) (X).begin(),(X).end()
#define sqr(X) ((X)*(X))

using namespace std;

typedef pair <int,int> pii;
typedef double ld;
typedef long long ll;
typedef pair <ll,ll> pll;
typedef vector<int> vi;
const int N=111111;
const ll P=1000000000;
const int INF=1111111111;
const double eps=1e-9;
const double pi=3.14159265358979;

double f[7][7][1<<12],p,ans;
int n,m,start,lim=1<<12,nxt;

int main(){
    cin>>n>>m;
    rep(i,n+m){
        int x;
        cin>>x;
        start|=1<<(x-1);
        if (x==13){
            puts("0.000000");
            return 0;
        }
    }
    cin>>p;
    f[n][m][start]=1.0;
    for (int sum=n+m;sum<=11;sum++)
        for (int win=n;win<=5;win++){
            int lose=sum-win;
            if (lose>5 || lose<m) continue;
            for (int msk=0;msk<lim;msk++){
                if (f[win][lose][msk]==0.0) continue;
                nxt=12;
                ans+=f[win][lose][msk]/13.0;
                for (int i=11;i>=0;i--){
                    if (!(msk&(1<<i))) nxt=i;
                    if (nxt==12) ans+=f[win][lose][msk]/13.0;
                    else{
                        f[win+1][lose][msk|(1<<nxt)]+=f[win][lose][msk]*p/13.0;
                        f[win][lose+1][msk|(1<<nxt)]+=f[win][lose][msk]*(1.0-p)/13.0;
                    }
                }
            }
        }
    printf("%lf\n",ans);
    return 0;
}