#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)

//* 便利な変数
namespace {
	int dx4[] = { 1, -1, 0, 0 };
	int dy4[] = { 0, 0, 1, -1 };

	int dx8[] = { 1, -1, 0, 0, 1, 1, -1, -1 };
	int dy8[] = { 0, 0, -1, 1, -1, 1, -1, 1 };

	int mDays[] = { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

	ll A, B, C, D, E, F, G, H, I, J, K, L, M,
		N, O, P, Q, R, S, T, U, V, W, X, Y, Z;
}
template <typename T>
vector<T> INP(ll n)
{
	vector<T> x;
	REP(i, n) {
		T tmp; cin >> tmp;
		x.push_back(tmp);
	}
	return move(x);
}
//* n文字1行の文字列を入力，一文字ごとの配列を返す
vector<char> SPRIT_STRING(ll n)
{
	string str; cin >> str;
	vector<char> cs(n);
	REP(i, n) cs[i] = str[i];
	return move(cs);
}
//* 文字列中から文字列を検索して別の文字列に置換する
void strReplace(std::string& str, const std::string& from, const std::string& to) {
	std::string::size_type pos = 0;
	while (pos = str.find(from, pos), pos != std::string::npos) {
		str.replace(pos, from.length(), to);
		pos += to.length();
	}
}
//* 素数判定 is_prime<unsigned>(N)
template<typename T, std::enable_if_t<std::is_unsigned<T>::value, std::nullptr_t> = nullptr>
bool is_prime(const T n) {
	if (n < 4) return n == 2 || n == 3;
	if (n % 2 == 0 || n % 3 == 0 || (n % 6 != 1 && n % 6 != 5)) return false;
	for (T i = 5; i * i <= n; i += 6) if (n % i == 0 || n % (i + 2) == 0) return false;
	return true;
}
//* 組み合わせ計算
inline unsigned long long NChooseK(const unsigned long long& n, const unsigned long long& k)
{
	if (n  < k) return 0;
	if (0 == n) return 0;
	if (0 == k) return 1;
	if (n == k) return 1;
	if (1 == k) return n;
	typedef unsigned long long value_type;
	value_type* table = new value_type[static_cast<std::size_t>(n * n)];
	std::fill_n(table, n * n, 0);
	class n_choose_k_impl
	{
	public:

		n_choose_k_impl(value_type* table, const value_type& dimension)
			: table_(table),
			dimension_(dimension)
		{}

		inline value_type& lookup(const value_type& n, const value_type& k)
		{
			return table_[dimension_ * n + k];
		}

		inline value_type compute(const value_type& n, const value_type& k)
		{
			if ((0 == k) || (k == n))
				return 1;
			value_type v1 = lookup(n - 1, k - 1);
			if (0 == v1)
				v1 = lookup(n - 1, k - 1) = compute(n - 1, k - 1);
			value_type v2 = lookup(n - 1, k);
			if (0 == v2)
				v2 = lookup(n - 1, k) = compute(n - 1, k);
			return v1 + v2;
		}

		value_type* table_;
		value_type dimension_;
	};
	value_type result = n_choose_k_impl(table, n).compute(n, k);
	delete[] table;
	return result;
}
//* 座標nx, nyがWidth,Heightの領域内にあるかどうかのチェック
inline bool rangeCheck2D(int nx, int ny, int Width, int Height)
{
	return nx >= 0 and nx < Width and ny >= 0 and ny < Height;
}
//* bit全探索
/*
for (int i = 0; i < 1<<N; i++) {
	REP(j, N)
		if ((1 & i >> j) == 1) {;}
}
*/

namespace arc062a {
	void arc062a()
	{
		cin >> N;
		ll ct, ca;
		REP(i, N) {
			ll t, a; cin >> t >> a;
			if (i == 0 or (t >= ct && a >= ca)) {
				ct = t; ca = a;
			}
			else {
				ll mult = 1, mula = 1;
				if (t < ct)
					mult = ct / t + ((ct%t == 0) ? 0 : 1);
				if (a < ca)
					mula = ca / a + ((ca%a == 0) ? 0 : 1);
				ll mulv = max(mult, mula);
				ct = t * mulv; ca = a * mulv;
			}
		}
		cout << ct + ca << endl;
	}
}

// 各辺を無効にしてみて幅優先探索
namespace abc075c {
	void abc075c()
	{
		cin >> N >> M;
		vector< pair<int, int> > es(M);
		for (auto& e : es) {
			int a, b; cin >> a >> b;
			e.first = a - 1;
			e.second = b - 1;
		}
		int cnt = 0;
		REP(disNum, M) {
			vector<bool> visited(N, false);
			queue<int> ps;
			ps.push(0);
			while (not ps.empty()) {
				int now = ps.front(); ps.pop();
				visited[now] = true;
				REP(i, M) {
					if (i == disNum) continue;
					pair<int, int> e = es[i];
					if (e.first == now and not(visited[e.second]))
						ps.push(e.second);
					if (e.second == now and not(visited[e.first]))
						ps.push(e.first);
				}
			}
			bool okay = true;
			REP(i, N)
				if (not visited[i]) {
					okay = false;
					break;
				}
			if (okay)
				cnt++;
		}
		cout << M - cnt << endl;
	}
}

namespace abc065c {
	bool dfs(int pos, string str)
	{
		if (pos == str.size()) return true;
		bool okay = false;
		if (pos + 7 <= str.size() and str.substr(pos, 7) == string("dreamer"))
			okay |= dfs(pos + 7, str);
		if (pos + 6 <= str.size() and str.substr(pos, 6) == string("eraser"))
			okay |= dfs(pos + 6, str);
		if (pos + 5 <= str.size()) {
			string five = str.substr(pos, 5);
			if (five == string("dream") or five == string("erase"))
				okay |= dfs(pos + 5, str);
		}
		return okay;
	}
	void abc065c()
	{
		string str; cin >> str;
		if (dfs(0, str))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
}

namespace abc066c {
	void abc066c()
	{
		cin >> N;
		vector<int> as(N);
		REP(i, N) cin >> as[i];
		sort(as.begin(), as.end());
		int n = as.size();
		ll ans = 1, pos, num;
		if (n % 2 == 0) {
			pos = 0; num = 1;
		}
		else {
			if (as[0] != 0) {
				cout << 0 << endl;
				return;
			}
			pos = 1; num = 2;
		}
		while (pos < n) {
			if (not (as[pos] == num and as[pos + 1] == num)) {
				cout << 0 << endl;
				return;
			}
			pos += 2; num += 2;
			ans *= 2;
			if (ans >= ((ll)1e9 + 7))
				ans -= (ll)1e9 + 7;
		}
		cout << ans << endl;
	}
}

int main()
{
	//abc079b::abc079b();
	abc066c::abc066c();
	//arc062a::arc062a();
	return 0;
}

Measured memory_bytes: 640