#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;

constexpr lint MOD = 1000000007;
vector<lint> fac, facInv, inv;
void facInit(int nmax)
{
    fac = facInv = inv = vector<lint>(nmax + 1, 1);
    for (int i = 2; i <= nmax; i++)
    {
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        facInv[i] = facInv[i-1] * inv[i] % MOD;
    }
}
lint nCr(lint n, lint r)
{
    if (n<r || r<0) return 0;
    if (n >= (int)fac.size()) facInit(n);
    return (fac[n] * facInv[r] % MOD) * facInv[n-r] % MOD;
}
lint nPr(lint n, lint r)
{
    if (n<r || r<0) return 0;
    if (n >= (int)fac.size()) facInit(n);
    return fac[n] * facInv[n-r] % MOD;
}
lint power(lint x, lint n, lint mod=MOD)
{
    lint ans = 1;
    while (n>0)
    {
        if (n & 1) (ans *= x) %= mod;
        (x *= x) %= mod;
       n >>= 1;
    }
   return ans;
}
lint doublefac(lint n)
{
    if (n < 0) return 0;
    lint k = (n + 1) / 2;
    if (n & 1) return fac[k * 2] * power(facInv[2], k) % MOD * power(fac[k], MOD - 2) % MOD;
    else return fac[k] * power(facInv[2], k) % MOD;
}
void No()
{
    puts("0");
    exit(0);
}


vector<set<int>> froms;
vector<int> to, toinv;
vector<int> we;

void dfs_cut(int now, int len)
{
    if (we[now]) No();
    int nxt = to[now];
    to[now] = -1;
    froms[nxt].erase(now);
    if (froms[nxt].size())
    {
        we[nxt] += len;
        return;
    }
    else dfs_cut(nxt, len + 1);
}

lint ret;

int main()
{
    facInit(200000);
    lint N;
    cin >> N;
    vector<int> A(N);
    cin >> A;
    froms.resize(N);
    to.resize(N);
    toinv.assign(N, -1);
    REP(i, N)
    {
        A[i]--;
        to[i] = A[i];
        froms[A[i]].insert(i);
    }
    we.resize(N);
    REP(i, N) if (froms[i].size() > 2) No();
    REP(i, N) if (froms[i].size() == 0)
    {
        dfs_cut(i, 1);
    }
    REP(i, N) if (to[i] >= 0) toinv[to[i]] = i;
    // dbg(we);
    ret = 1;
    map<int, int> circle_cnt;
    vector<int> visited(N);
    // dbg(to);
    // dbg(toinv);
    // dbg(we);

    REP(r, N) if (!visited[r] and toinv[r] >= 0)
    {
        bool www = false;
        int now = r;
        int circlelength = 0;
        while (true)
        {
            visited[now] = 1;
            if (we[now] > 0)
            {
                www = true;
                int l = 0;
                int tmp = now;
                while (true)
                {
                    l++;
                    tmp = toinv[tmp];
                    if (we[tmp] > 0) break;
                }
                if (l > we[now]) ret = ret * 2 % MOD;
                else if (l < we[now]) ret = 0;
            }
            now = toinv[now];
            circlelength++;
            if (visited[now]) break;
        }
        if (!www)
        {
            circle_cnt[circlelength]++;
        }
    }

    for (auto p : circle_cnt)
    {
        lint n = p.second;
        lint fa = 0;
        REP(pair, n / 2 + 1)
        {
            int rem = n - pair * 2;
            lint remfac = ((p.first % 2) and p.first > 2) ? power(2, rem) : 1;
            fa += remfac * nCr(n, pair * 2) % MOD * (pair == 0 ? 1 : doublefac(pair * 2 - 1)) % MOD * power(p.first, pair) % MOD;
        }
        // dbg(p);
        // dbg(fa);
        ret = ret * (fa % MOD) % MOD;
    }
    cout << ret << endl;
}


Measured memory_bytes: 16256