// (⁠◕⁠ᴗ⁠◕⁠✿⁠)
 
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define srep(i, s, n) for (ll i = s; i < (n); i++)
#define len(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
using namespace std;
template<typename T> using vc = vector<T>;
template<typename T> using vv = vc<vc<T>>;
template<typename T> using vvv = vv<vc<T>>;
using vi = vc<int>;using vvi = vv<int>; using vvvi = vv<vi>;
using ll = long long;using vl = vc<ll>;using vvl = vv<ll>; using vvvl = vv<vl>;
using ld = long double; using vld = vc<ld>; using vvld = vc<vld>; using vvvld = vc<vvld>;
using uint = unsigned int;
using ull = unsigned long long;
const ld pi = acos(-1.0);
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
// const ll mod = 1000000007;
const ll mod = 998244353;
inline bool inside(ll y, ll x, ll H, ll W) {return 0 <= (y) and (y) < (H) and 0 <= (x) and (x) < (W); }
 
#define debug(var)  do{std::cout << #var << " : \n";view(var);}while(0)
template<typename T> void view(T e){cout << e << endl;}
template<typename T> void view(const vc<T>& v){for(const auto& e : v){ cout << e << " "; } cout << endl;}
template<typename T> void view(const vv<T>& vv){ for(const auto& v : vv){ view(v); } }

int main(){
    int N; cin >> N;
    vi A(N); rep(i, N) cin >> A[i];
    sort(all(A));
    if (N > 13){
        int sm = accumulate(all(A), 0);
        int ans = -1;
        rep(i, N - 1) if (A[i] == A[i + 1]){
            ans = max(sm - 2 * A[i], ans);
        }
        set<int> can;
        rep(j, N){
            if (can.count(A[j])) ans = max(sm - 2 * A[j], ans);
            rep(i, j) can.insert(A[i] + A[j]);
        }
        cout << ans << endl;
        return 0;
    }
    vi pw(14, 1); rep(i, 13) pw[i + 1] = pw[i] * 3;
    int ans = -1;
    rep(cmb, pw[N]){
        vi cnt(3, 0);
        rep(i, N) cnt[cmb / pw[i] % 3] += A[i];
        if (cnt[0] == cnt[1] && cnt[0] > 0 && cnt[2] > 0) ans = max(ans, cnt[2]);
    }
    cout << ans << endl;
}