#line 1 "lib/template.hpp"
#ifdef TEMPLATE
#else
#define TEMPLATE
# pragma GCC optimize("O3")
using namespace std;
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <algorithm>
#include <numeric>
#include <cmath>
#include <climits>
#include <cassert>
#include <functional>
#include <iterator>
#include <utility>
#include <complex>
#include <bitset>
#include <chrono>
#include <random>
#include <limits>
#include <optional>
#include <variant>
#include <any>

#include <array>
#include <bit>
#include <compare>
#include <concepts>
#include <numbers>
#include <ranges>
#include <span>
#include <string_view>
#include <tuple>
#include <type_traits>
#include <version>
using uint=unsigned;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
using i128=__int128;
template<class T>using vc=vector<T>;
template<class T>using vvc=vc<vc<T>>;
template<class T>using vvvc=vvc<vc<T>>;
template<class T>using smpq=priority_queue<T,vector<T>,greater<T>>;
template<class T>using bipq=priority_queue<T>;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define REP(i,j,n) for(ll i=(j);i<(ll)(n);i++)
#define DREP(i,n,m) for(ll i=(n);i>=(m);i--)
#define drep(i,n) for(ll i=((n)-1);i>=0;i--)
#define rall(x) x.rbegin(),x.rend()
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define is insert
#define bg begin()
#define ed end()
#define all(x) x.begin(),x.end()
void scan(int&a) { cin >> a; }
void scan(ll&a) { cin >> a; }
void scan(string&a) { cin >> a; }
void scan(char&a) { cin >> a; }
void scan(uint&a) { cin >> a; }
void scan(ull&a) { cin >> a; }
void scan(bool&a) { cin >> a; }
void scan(ld&a){ cin>> a;}
template<class T> void scan(vector<T>&a) { for(auto&x:a) scan(x); }
void read() {}
template<class Head, class... Tail> void read(Head&head, Tail&... tail) { scan(head); read(tail...); }
#define INT(...) int __VA_ARGS__; read(__VA_ARGS__);
#define LL(...) ll __VA_ARGS__; read(__VA_ARGS__);
#define ULL(...) ull __VA_ARGS__; read(__VA_ARGS__);
#define STR(...) string __VA_ARGS__; read(__VA_ARGS__);
#define VC(type, name, ...) vector<type> name(__VA_ARGS__); read(name);
#define VVC(type, name, size, ...) vector<vector<type>> name(size, vector<type>(__VA_ARGS__)); read(name);
template<class T>void print(T a) { cout << a; }
template<class T> void print(vector<T>a) { for(int i=0;i<(int)a.size();i++){if(i)cout<<" ";print(a[i]);}cout<<endl;}
void PRT() { cout <<endl; return ; }
template<class T> void PRT(T a) { print(a); cout <<endl; return; }
template<class Head, class... Tail> void PRT(Head head, Tail ... tail) { print(head); cout << " "; PRT(tail...); return; }
template<class T,class F>
bool chmin(T &x, F y){
    if(x>y){
        x=y;
        return true;
    }
    return false;
}
template<class T, class F>
bool chmax(T &x, F y){
    if(x<y){
        x=y;
        return true;
    }
    return false;
}
template <typename T>
T floor(T a, T b) {
  return a / b - (a % b && (a ^ b) < 0);
}
template <typename T>
T ceil(T x, T y) {
  return floor(x + y - 1, y);
}
template <typename T>
T bmod(T x, T y) {
  return x - y * floor(x, y);
}
template <typename T>
pair<T, T> divmod(T x, T y) {
  T q = floor(x, y);
  return {q, x - q * y};
}
void YesNo(bool b){
    cout<<(b?"Yes":"No")<<endl;
}
void YESNO(bool b){
    cout<<(b?"YES":"NO")<<endl;
}
void AliceBob(bool b){
    cout<<(b?"Alice":"Bob")<<endl;
}
void TakahashiAoki(bool b){
    cout<<(b?"Takahashi":"Aoki")<<endl;
}
void Yes(){
    cout<<"Yes"<<endl;
}
void No(){
    cout<<"No"<<endl;
}
vc<int>stovi(const string&s,const string&S){
    vc<int>v(s.size());
    rep(i,s.size()){
        auto t=S.find(s[i]);
        assert(t!=string::npos);
        v[i]=t;
    }
    return v;
}
template<class T=ll>
T isqrt(T x){
    T F=sqrtl(x);
    while((F+1)*(F+1)<=x)F++;
    while(F*F>x)F--;
    return F;
}
template<class T>
vvc<T>trans(const vvc<T>&a){
    assert(a.size()&&a[0].size());
    vvc<T>b(a[0].size(),vc<T>(a.size()));
    rep(i,a.size())rep(j,a[0].size()){
        b[j][i]=a[i][j];
    }
    return b;
}
template<class T>
vc<string>trans(const vc<string>&a){
    assert(a.size()&&a[0].size());
    vc<string>b(a[0].size(),string(a.size(),0));
    rep(i,a.size())rep(j,a[0].size()){
        b[j][i]=a[i][j];
    }
    return b;
}
template<class T>
int popcount(T n){
    return __builtin_popcountll(n);
}
template<class T,class L=ll>
L sum(vc<T>&a){
    return accumulate(all(a),L(0));
}
template<class T>
vc<T>subset(T S){
    vc<T>ans;
    for(T x=S;x>0;x=(x-1)&S)ans.pb(x);
    ans.pb(0);
    return ans;
}
template<class T>
T max(vc<T>&a){
    return *max_element(all(a));
}
template<class T>
T min(vc<T>&a){
    return *min_element(all(a));
}
#ifndef COMPRESSER_STRUCT
#define COMPRESSER_STRUCT
template<class T>
struct Compresser{
    vc<T>x;
    Compresser(int n=0){x.reserve(n);}
    Compresser(const vc<T>&xs){
        x=xs;
    }
    void push(T p){built=false;x.pb(p);}
    bool built=false;
    void build(){
        if(!chmax(built,1))return;
        sort(all(x));
        x.erase(unique(all(x)),x.end());
    }
    int find(T v){
        build();
        auto itr=lower_bound(all(x),v)-x.begin();
        if(itr==x.size()||x[itr]!=v)return -1;
        return itr;
    }
    int find_next(T v){
        build();
        return lower_bound(all(x),v)-x.begin();
    }
    int size(){
        build();
        return x.size();
    }
    T operator[](int i)const{
        assert(0<=i&&i<x.size());
        return x[i];
    }
};
#endif
template<class T,class L=ll>
vc<L> presum(vc<T> &a){
    vc<L> ret(a.size()+1);
    rep(i,a.size())ret[i+1]=ret[i]+a[i];
    return ret;
}
template<class T, class F>
vc<T> &operator+=(vc<T> &a,F b){
    for (auto&v:a)v += b;
    return a;
}
template<class T, class F>
vc<T> &operator-=(vc<T>&a,F b){
    for (auto&v:a)v-=b;
    return a;
}
template<class T, class F>
vc<T> &operator*=(vc<T>&a,F b){
    for (auto&v:a)v*=b;
    return a;
}
template<class T=ll>
constexpr T POW(T a,T b){
    T res=1;
    while(b){
        if(b&1)res*=a;
        a*=a;
        b/=2;
    }
    return res;
}
constexpr ll ten(ll a){
    return POW<ll>(10,a);
}
template<typename T>constexpr T inf=numeric_limits<T>::max()/2-1;
template<class T>
int tbit(T x){
    using U=make_unsigned_t<T>;
    U y=(U)x;
    return y?(int)bit_width(y)-1:-1;
}
template<class T>
int lbit(T x){
    using U=make_unsigned_t<T>;
    U y=(U)x;
    return y?(int)countr_zero(y):-1;
}
template<class T>
int tbit(T x,int p){
    using U=make_unsigned_t<T>;
    constexpr int W=numeric_limits<U>::digits;
    U y=(U)x;
    if(p<0)return -1;
    if(p>=W-1)return tbit(y);
    return tbit(y&((U(1)<<(p+1))-1));
}
template<class T>
int lbit(T x,int p){
    using U=make_unsigned_t<T>;
    constexpr int W=numeric_limits<U>::digits;
    U y=(U)x;
    if(p<0)return lbit(y);
    if(p>=W)return -1;
    return lbit(y&(~U(0)<<p));
}
istream& operator>>(istream&is,i128&x){
    string s;is>>s;
    x=0;
    int i=0,neg=0;
    if(s[0]=='-')neg=1,i=1;
    for(;i<(int)s.size();i++)x=x*10+s[i]-'0';
    if(neg)x=-x;
    return is;
}
ostream& operator<<(ostream&os,i128 x){
    if(x==0)return os<<0;
    if(x<0)os<<"-";
    using u128=__uint128_t;
    u128 y=x<0?-(u128)x:(u128)x;
    string s;
    while(y)s.pb('0'+y%10),y/=10;
    reverse(all(s));
    return os<<s;
}
#define dbg(...) 1111

#ifdef LOCAL
#undef dbg

template<class T,class U>
ostream& operator<<(ostream&os,const pair<T,U>&p){
    return os<<"("<<p.fi<<", "<<p.se<<")";
}
template<class T,size_t N>
ostream& operator<<(ostream&os,const array<T,N>&a){
    os<<"[";
    rep(i,N){
        if(i)os<<", ";
        os<<a[i];
    }
    return os<<"]";
}
template<class T>
ostream& operator<<(ostream&os,const vc<T>&a){
    os<<"[";
    rep(i,a.size()){
        if(i)os<<", ";
        os<<a[i];
    }
    return os<<"]";
}
template<class T>
ostream& operator<<(ostream&os,const deque<T>&a){
    os<<"[";
    rep(i,a.size()){
        if(i)os<<", ";
        os<<a[i];
    }
    return os<<"]";
}
template<class T>
ostream& operator<<(ostream&os,const set<T>&s){
    os<<"{";
    bool f=0;
    for(auto&x:s){
        if(f)os<<", ";
        f=1;
        os<<x;
    }
    return os<<"}";
}
template<class T>
ostream& operator<<(ostream&os,const multiset<T>&s){
    os<<"{";
    bool f=0;
    for(auto&x:s){
        if(f)os<<", ";
        f=1;
        os<<x;
    }
    return os<<"}";
}
template<class T>
ostream& operator<<(ostream&os,const unordered_set<T>&s){
    os<<"{";
    bool f=0;
    for(auto&x:s){
        if(f)os<<", ";
        f=1;
        os<<x;
    }
    return os<<"}";
}
template<class T,class U>
ostream& operator<<(ostream&os,const map<T,U>&m){
    os<<"{";
    bool f=0;
    for(auto&x:m){
        if(f)os<<", ";
        f=1;
        os<<x;
    }
    return os<<"}";
}
template<class T,class U>
ostream& operator<<(ostream&os,const unordered_map<T,U>&m){
    os<<"{";
    bool f=0;
    for(auto&x:m){
        if(f)os<<", ";
        f=1;
        os<<x;
    }
    return os<<"}";
}
template<class T>
ostream& operator<<(ostream&os,queue<T>q){
    vc<T>a;
    while(q.size())a.pb(q.front()),q.pop();
    return os<<a;
}
template<class T>
ostream& operator<<(ostream&os,stack<T>s){
    vc<T>a;
    while(s.size())a.pb(s.top()),s.pop();
    return os<<a;
}
template<class T,class C,class F>
ostream& operator<<(ostream&os,priority_queue<T,C,F>q){
    vc<T>a;
    while(q.size())a.pb(q.top()),q.pop();
    return os<<a;
}

void debug_out(){cout<<endl;}
template<class T,class... Ts>
void debug_out(const T&x,const Ts&...xs){
    cout<<x;
    if constexpr(sizeof...(xs))cout<<" ",debug_out(xs...);
    else cout<<endl;
}
#define dbg(...) cout<<"["<<#__VA_ARGS__<<"] = ",debug_out(__VA_ARGS__)
#endif

struct TemplateSetup{
    TemplateSetup(){
        #ifdef LOCAL
        freopen("input.txt","r",stdin);
        freopen("output.txt","w",stdout);
        
        #endif
        cin.tie(0)->sync_with_stdio(0);
        #ifdef LOCAL
        cout<<fixed<<setprecision(6);
        dbg("==============="s);
        #else
        cout<<fixed<<setprecision(20);
        #endif
    }
};
inline TemplateSetup template_setup;

#endif
#line 2 "b.cpp"
void solve(){
    INT(n);
    VC(ld,a,n);
    vc<ll>pw(n+1);pw[0]=1;rep(i,n)pw[i+1]=pw[i]*3;
    vc<ld>dpa(pw[n]);
    vc<ld>dpb(pw[n]);
    //0 -> まだ
    //1 -> Alice が取った
    //2 -> Bob が取った
    drep(bit,pw[n]){
        ll done=1;
        rep(j,n){
            int A=bit/pw[j]%3;
            done&=!!A;
        }
        if(done){
            ll alice=0;
            rep(j,n){
                if(bit/pw[j]%3==1){
                    alice+=a[j];
                }else{
                    alice-=a[j];
                }
            }
            if(alice>0)dpa[bit]=dpb[bit]=1;
            continue;
        }
        {
            ld l=0,r=1;
            rep(t,30){
                ld m=(l+r)/2;
                auto vv=[&](ld tar){
                    ld tmp=0;
                    rep(k,n){
                        if(bit/pw[k]%3==0){
                            ld tmp2=1e9;
                            rep(l,n){
                                if(bit/pw[l]%3==0){
                                    chmin(tmp2,dpa[bit+pw[l]*2]/a[l]+(a[l]-1)/a[l]*tar);
                                }
                            }
                            chmax(tmp,dpb[bit+pw[k]]/a[k]+(a[k]-1)/a[k]*tmp2);
                        }
                    }
                    return tmp;
                };
                if(vv(m)-m>=0){
                    l=m;
                }else{
                    r=m;
                }
            }
            dpa[bit]=l;
            dpb[bit]=1;
            rep(k,n){
                if(bit/pw[k]%3==0){
                    chmin(dpb[bit],dpa[bit+pw[k]*2]/a[k]+(a[k]-1)/a[k]*dpa[bit]);
                }
            }
        }
    }
    PRT(dpa[0]);
}
signed main(){
    int t=1;
    // cin >> t;
    while(t--)solve();
}