#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
// #define int long long
// #define double long double
#define rep(i,n) for (int i=0; i<(int)(n); ++i)
#define rep1(i,n) for (int i=1; i<(int)(n); ++i)
#define repeq(i,n) for (int i=0; i<=(int)(n); ++i)
#define rep1eq(i,n) for (int i=1; i<=(int)(n); ++i)
#define rrep(i,n) for (int i=(int)(n)-1; i>=0; --i)
#define rrep1(i,n) for (int i=(int)(n)-1; i>0; --i)
#define rrepeq(i,n) for (int i=(int)(n); i>=0; --i)
#define rrep1eq(i,n) for (int i=(int)(n); i>0; --i)
#define REP(i,a,b) for (int i=(int)(a); i<=(int)(b); ++i)
#define RREP(i,a,b) for (int i=(int)(a); i>=(int)(b); --i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using vb = vector<bool>;
template<typename T> using Graph = vector<vector<T>>;
template<typename T> using Spacial = vector<vector<vector<T>>>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int MOD = 1e9+7;
const int MOD2 = 998244353;
// const double EPS = 1e-9;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
string interval[2] = {" ", "\n"}; // {" ", "\n"}

template<typename T> struct is_plural : false_type{};
template<typename T1, typename T2> struct is_plural<pair<T1, T2>> : true_type{};
template<typename T> struct is_plural<vector<T>> : true_type{};
template<typename T> struct is_plural<complex<T>> : true_type{};
 
template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << " " << p.second; }
template<typename T> istream &operator>>(istream &is, vector<T> &vec) { for (auto itr = vec.begin(); itr != vec.end(); ++itr) is >> *itr; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec) { if (vec.empty()) return os; bool pl = is_plural<T>(); os << vec.front(); for (auto itr = ++vec.begin(); itr != vec.end(); ++itr) os << interval[pl] << *itr; return os; }
 
bool CoutYN(bool a, string y = "Yes", string n = "No") { cout << (a ? y : n) << "\n"; return a; }

template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

long long modpow(int a, long long n, int mod = MOD) { long long ret = 1; do { if (n & 1) ret = ret * a % mod; a = 1LL * a * a % mod; } while (n >>= 1); return ret; }

template<typename T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
template<typename T> T LCM(T a, T b) { return a / GCD(a, b) * b; }

template<typename T1, typename T2> bool CompareBySecond(pair<T1, T2> a, pair<T1, T2> b) { return a.second != b.second ? a.second < b.second : a.first < b.first; }


/* -------- <templates end> -------- */


stack<int> hist;
vi cycle;
vb seen, finished;

vector<pii> grundy;

void predfs(Graph<int> &g, int v) {
  hist.push(v);
  seen[v] = true;

  for (auto &nv : g[v]) {
    if (finished[nv]) continue;

    if (seen[nv]) {
      cycle.emplace_back(nv);

      while (hist.top() != nv) {
        cycle.emplace_back(hist.top());
        hist.pop();
      }

      return;
    }

    predfs(g, nv);

    if (!cycle.empty()) return;
  }

  hist.pop();
  finished[v] = true;
}

int dfs(Graph<int> &g, int v, int p = -1) {
  int sz = g[v].size();
  vb det(sz + 1, false);

  for (auto &nv : g[v]) {
    if (nv != p) {
      int ret = dfs(g, nv);
      if (ret < sz) det[ret] = true;
    }
  }

  int tmp = -1;

  repeq(i,sz) {
    if (!det[i]) {
      if (p == -1) return i;

      if (tmp == -1) {
        tmp = i;
        continue;
      }

      grundy.emplace_back(tmp, i);
      return 0;
    }
  }
}

int confirm(int idx, int next) {
  if (idx == grundy.size()) return next;

  int prev = grundy[idx].first == next ? grundy[idx].second : grundy[idx].first;
  return confirm(idx + 1, prev);
}

void solve() {
  int n; cin >> n;

  Graph<int> g(n);
  rep(i,n) {
    int v; cin >> v; --v;
    g[v].emplace_back(i);
  }

  seen.assign(n, false);
  finished.assign(n, false);

  rep(i,n) {
    if (!seen[i]) predfs(g, i);
    if (!cycle.empty()) break;
  }

  const int sz = cycle.size();
  grundy.reserve(sz);

  int prev = cycle.back();

  for (auto &v : cycle) {
    dfs(g, v, prev);
    prev = v;
  }

  bool p = grundy.back().first == confirm(0, grundy.back().first);
  if (!p) p = grundy.back().second == confirm(0, grundy.back().second);

  CoutYN(p, "POSSIBLE", "IMPOSSIBLE");
}


/* -------- <programs end> -------- */


signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  solve();
  return 0;
}


Measured memory_bytes: 26164