/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author aajisaka
 */


#include<bits/stdc++.h>

using namespace std;

void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

#define SPEED ios_base::sync_with_stdio(false);cin.tie(nullptr)
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define all(v) v.begin(), v.end()
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

using ll = long long;
using ull = unsigned long long;
using P = pair<ll, ll>;

constexpr long double PI = 3.14159265358979323846264338327950288L;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

class No1237EXPMultiple {
public:
    void solve(istream& cin, ostream& cout) {
      SPEED;
      int n; cin >> n;
      // 0^(0!) = 0
      // 1^(1!) = 1
      // 2^(2!) = 4
      // 3^(3!) = 3^6 = 27*27
      // 4^(4!) = 4^16 = 2^32 > 10^9 + 7
      vector<ll> a(n);
      rep(i, n) {
        cin >> a[i];
        if (a[i] == 0) {
          cout << -1 << endl;
          return;
        }
      }

      int mod = 1e9+7;

      ll multiple = 1;
      rep(i, n) {
        if (a[i] >= 4) {
          cout << mod << '\n';
          return;
        }
        if (a[i] == 2) {
          multiple *= 4;
        } else if (a[i] == 3) {
          multiple *= 27*27;
        }
        if (multiple > mod) {
          cout << mod << '\n';
          return;
        }
      }

      cout << mod%multiple << '\n';
    }
};

signed main() {
  No1237EXPMultiple solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}