#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

int nxt[3000 * 5000 + 1];

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  memset(nxt, -1, sizeof(nxt));
  nxt[0] = 0;
  int n;
  cin >> n;
  VI a(n);
  rep(i, n) cin >> a[i];
  constexpr int INF = 1001001001;
  int ans = INF;
  for (int i = 0, end = 3000 * 5000; i < end; i++) {
    if (nxt[i] >= 0) {
      for (int j = nxt[i]; j < n; j++) {
        int ni = i + a[j];
        if (nxt[ni] != -1) {
          chmin(ans, ni);
          chmin(end, ni);
          break;
        } else {
          nxt[ni] = j + 1;
        }
      }
    }
  }
  if (ans == INF) {
    ans = -1;
  } else {
    ans = accumulate(all(a), 0) - 2 * ans;
    if (ans == 0) ans = -1;
  }
  cout << ans << '\n';
}