#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>
#include <random>
#include <chrono>
#include <cassert>
#include <tuple>
#include <utility>
using namespace std;

namespace {
  using Integer = long long; //__int128;
  template<class T, class S> istream& operator >> (istream& is, pair<T,S>& p){return is >> p.first >> p.second;}
  template<class T> istream& operator >> (istream& is, vector<T>& vec){for(T& val: vec) is >> val; return is;}
  template<class T> istream& operator ,  (istream& is, T& val){ return is >> val;}
  template<class T, class S> ostream& operator << (ostream& os, const pair<T,S>& p){return os << p.first << " " << p.second;}
  template<class T> ostream& operator << (ostream& os, const vector<T>& vec){for(size_t i=0; i<vec.size(); i++) os << vec[i] << (i==vec.size()-1?"":" "); return os;}
  template<class T> ostream& operator ,  (ostream& os, const T& val){ return os << " " << val;}

  template<class H> void print(const H& head){ cout << head; }
  template<class H, class ... T> void print(const H& head, const T& ... tail){ cout << head << " "; print(tail...); }
  template<class ... T> void println(const T& ... values){ print(values...); cout << endl; }

  template<class H> void eprint(const H& head){ cerr << head; }
  template<class H, class ... T> void eprint(const H& head, const T& ... tail){ cerr << head << " "; eprint(tail...); }
  template<class ... T> void eprintln(const T& ... values){ eprint(values...); cerr << endl; }

  class range{ Integer start_, end_, step_; public: struct range_iterator{ Integer val, step_; range_iterator(Integer v, Integer step) : val(v), step_(step) {} Integer operator * (){return val;} void operator ++ (){val += step_;} bool operator != (range_iterator& x){return step_ > 0 ? val < x.val : val > x.val;} }; range(Integer len) : start_(0), end_(len), step_(1) {} range(Integer start, Integer end) : start_(start), end_(end), step_(1) {} range(Integer start, Integer end, Integer step) : start_(start), end_(end), step_(step) {} range_iterator begin(){ return range_iterator(start_, step_); } range_iterator   end(){ return range_iterator(  end_, step_); } };

  inline string operator "" _s (const char* str, size_t size){ return move(string(str)); }
  constexpr Integer my_pow(Integer x, Integer k, Integer z=1){return k==0 ? z : k==1 ? z*x : (k&1) ? my_pow(x*x,k>>1,z*x) : my_pow(x*x,k>>1,z);}
  constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z=1){return k==0 ? z%M : k==1 ? z*x%M : (k&1) ? my_pow_mod(x*x%M,k>>1,M,z*x%M) : my_pow_mod(x*x%M,k>>1,M,z);}
  constexpr unsigned long long operator "" _ten (unsigned long long value){ return my_pow(10,value); }

  inline int k_bit(Integer x, int k){return (x>>k)&1;} //0-indexed

  mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count());

  template<class T> string join(const vector<T>& v, const string& sep){ stringstream ss; for(size_t i=0; i<v.size(); i++){ if(i>0) ss << sep; ss << v[i]; } return ss.str(); }

  inline string operator * (string s, int k){ string ret; while(k){ if(k&1) ret += s; s += s; k >>= 1; } return ret; }
}
constexpr long long mod = 9_ten + 7;

class SCC{
  int n;
  vector<vector<int> > G;
  vector<vector<int> > rG;
  
  void dfs(vector<bool> &visit, int pos, vector<int> &result){
    visit[pos] = true;
    for(int i=0; i<G[pos].size(); i++){
      if(visit[ G[pos][i] ]) continue;
      dfs(visit, G[pos][i], result);
    }
    result.push_back(pos);
  }

  void rdfs(vector<bool> &visit, int pos, int k){
    visit[pos] = true;
    component[pos] = k;
    for(int i=0; i<rG[pos].size(); i++){
      if(visit[ rG[pos][i] ]) continue;
      rdfs(visit, rG[pos][i], k);
    }
  }

  void make_rev(vector<vector<int> > &G){
    for(int i=0; i<n; i++){
      for(int j=0; j<G[i].size(); j++){
        rG[ G[i][j] ].push_back(i);
      }
    }
  }

 public:
  int num_components;
  vector<int> component;
  vector< vector<int> > scc_graph;
  
  SCC(int n){
    this->n = n;
    G.resize(n);
    rG.resize(n);
  }

  SCC(vector<vector<int> > &G){
    this->n = G.size();
    this->G = G;
    rG.resize(n);
    make_rev(G);
  }
  
  void strongly_connected_components(){
    vector<bool> visit(n, false);
    vector<int> result;

    for(int i=0; i<n; i++){
      if(visit[i]) continue;
      dfs(visit, i, result);
    }

    
    component.resize(n);
    fill(visit.begin(), visit.end(), false);
    int k=0;
    for(int i=result.size()-1; i>=0; i--){
      if(visit[ result[i] ]) continue;
      rdfs(visit, result[i], k);
      k++;
    }

    num_components = k;
    scc_graph.resize( num_components );
    for(int i=0; i<n; i++){
      int cmp = component[i];
      for(int j=0; j<G[i].size(); j++){
        if(component[ G[i][j] ] == cmp) continue;
        scc_graph[cmp].push_back( component[ G[i][j] ] );
      }
    }
    
    for(int i=0; i<scc_graph.size(); i++){
      sort(scc_graph[i].begin(), scc_graph[i].end());
      scc_graph[i].erase( unique(scc_graph[i].begin(), scc_graph[i].end()), scc_graph[i].end());
    }
    
  }
  
  void add_edge(int from, int to){
    G[from].push_back(to);
    rG[to].push_back(from);
  }
};

vector<vector<int>> cc;
vector<int> comp;

int dfs(vector<vector<int>>& G, vector<int>& c, int pos, int par){
  if( c[pos] != -1 ) return c[pos];

  int res = 0;
  set<int> x;
  for(auto nx : G[pos]){
    if( nx == par ) continue;
    if( comp[nx] == comp[pos] ) continue;
    int tmp = dfs(G,c,nx,pos);
    x.insert( tmp );
  }

  while( x.count(res) ) res++;

  c[pos] = res;
  return res;
}



int main(){
  int n;
  cin >> n;

  vector<int> p(n);
  cin >> p;

  vector<vector<int>> G(n);
  vector<int> out(n, 0);
  for(int i=0; i<n; i++){
    out[ p[i]-1 ]++;
    G[p[i]-1].push_back(i);
  }

  SCC scc(n);
  for(int i=0; i<n; i++){
    scc.add_edge(p[i]-1, i);
  }
  scc.strongly_connected_components();

  comp = scc.component;
  cc.resize(scc.num_components);
  for(int i=0; i<n; i++){
    cc[ scc.component[i] ].push_back( i );
  }

  int loop_comp = -1;
  for(int i=0; i<cc.size(); i++){
    if( cc[i].size() > 1 ){
      loop_comp = i;
    }
  }

  if( cc[loop_comp].size()%2 == 0 ){
    println("POSSIBLE");
    return 0;
  }

  vector<int> color(n,-1);
  for(auto v : cc[loop_comp]){
    dfs( G,color,v,-1 );
  }

  for(int i=1; i<cc[loop_comp].size(); i++){
    int v = cc[loop_comp][i];
    int u = cc[loop_comp][i-1];
    if( color[v] != color[u] ){
      println("POSSIBLE");
      return 0;
    }
  }

  println("IMPOSSIBLE");

  return 0;
}


Measured memory_bytes: 46360