#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
typedef long long ll;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#define ios ios_base::sync_with_stdio(0) ; cin.tie(0) ; cout.tie(0)
#define so sizeof
#define pb push_back
#define cl clear() ;
#define vl vector<ll>
#define sz size()
#define len length()
#define emp empty()
#define el endl;cout.flush()
#define be begin()
#define fi first
#define se second
#define br break
#define en end()
#define ro return 0
#define br break
#define eb emplace_back
#define con continue
#define ms(x) memset(x , 0, so x)
#define all(x) (x).be , (x).en
#define acc(x) accumulate((x).be , (x).en , 0ll)
#define forn(i,a,b) for(ll i=a;i<=b;++i)
#define rng_58 mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())
#define vll vector<pair<ll,ll> >
#define pll pair<ll,ll>
#define plll pair<ll,pair<ll,ll>>
#define plvl pair<pair<ll,ll> ,ll>
#define mp make_pair
#define trace3(a,b,c) cerr <<"a is " << a << " b is " << b << " c is " << c << el;
#define trace4(a,b,c,d) cerr <<"a is " << a << " b is " << b << " c is " << c <<" d is " << d << el ;
#define trace5(a,b,c,d,e) cerr <<"a is " << a << " b is " << b << " c is " << c <<" d is " << d << " e is " << e << el;
#define trace6(a,b,c,d,e,f) cerr <<"a is " << a << " b is " << b << " c is " << c <<" d is " << d << " e is " << e << " f is " << f << el ;
const ll mod = 1e9 + 7 ;
int main()
{
    ios;
    ll n ;
    cin >> n ;
    vl v;
    unordered_map<ll , ll > mpp ;
    forn(i , 1 , n ) {
      ll x;
      cin >> x;
      v.pb(x) ;
      mpp[x]++;
    }
    if(n % 2 == 1){
        ll from = 0 , till = n - 1 ;
        forn(i , from , till){
           if(i == 0 ){
             if(mpp[i]!=1){
                cout << 0 << el ;
                ro ;
             }
           }
           else{
            if(mpp[i] != 2){
                cout << 0  << el ;
                ro ;
            }
           }
           ++i ;
        }
        if(n == 1){
            cout << 1 << el ;
            ro ;
        }
        else {
            ll ans = 1 ;
            from = 2;
            till = n-1 ;
            forn(i , from ,till){
               ans = ans * 2 ;
               ans%= mod ;
               ++i;
            }
           cout << ans << el ;
           ro ;
        }
    }
    else if(n % 2 == 0 ) {
           ll from = 1 , till = n-1 ;
           forn(i , from , till){
              if(mpp[i]!= 2){
                cout << 0 << el ;
                ro ;
              }
              ++i ;
           }
           if(n == 2){
            cout << 2 << el ;
            ro ;
           }
           else if(n > 2 ) {
              ll ans = 2 ;
              from = 3;
              till = n-1 ;
              forn(i , from ,till){
                 ans = ans * 2 ;
                 ans%= mod ;
                 ++i;
              }
              cout << ans << el ;
              ro ;
           }
    }
    ro ;
}



Measured memory_bytes: 4484