#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#include<cassert>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define reps(X,S,Y) for (int (X) = S;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y)-1;(X) >=0;--(X))
#define rreps(X,S,Y) for (int (X) = (Y)-1;(X) >= (S);--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define eb emplace_back
#define UNIQUE(X) (X).erase(unique(all(X)),(X).end())
#define Endl endl

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> using vv=vector<vector<T>>;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
#define out(args...){vector<string> a_r_g_s=s_p_l_i_t(#args, ','); e_r_r(a_r_g_s.begin(), args); }
vector<string> s_p_l_i_t(const string &s, char c){vector<string> v;int d=0,f=0;string t;for(char c:s){if(!d&&c==',')v.pb(t),t="";else t+=c;if(c=='\"'||c=='\'')f^=1;if(!f&&c=='(')++d;if(!f&&c==')')--d;}v.pb(t);return move(v);}
void e_r_r(vector<string>::iterator it) {}
template<typename T, typename... Args> void e_r_r(vector<string>::iterator it, T a, Args... args){ if(*it==" 1"||*it=="1") cerr<<endl; else cerr << it -> substr((*it)[0] == ' ', it -> length()) << " = " << a << ", "; e_r_r(++it, args...);}
const ll MOD=1e9+7;

struct UF{
  vector<int> data;
  UF(int size):data(size,-1){}
  bool unite(int x,int y){
    x=root(x); y=root(y);
    if(x!=y){
      if(data[y]<data[x]) swap(x,y);
      data[x]+=data[y]; data[y]=x;
    }
    return x!=y;
  }
  bool findSet(int x,int y){return root(x)==root(y);}
  int root(int x){return data[x]<0?x:data[x]=root(data[x]);}
  int size(int x) {return -data[root(x)];}
};

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
  int n;
  cin>>n;
  vv<int> g(n);
  vv<int> h(n);
  vector<int> lps;
  UF uf(n);
  rep(i,n){
    int x;
    cin>>x; --x;
    //out(x,i,1);
    if(uf.unite(x,i)==0){
      for(int v=x;v!=i;v=h[v][0]) lps.pb(v);
      lps.pb(i);
    }
    g[x].pb(i);
    h[i].pb(x);
  }
  //out(lps,1);
  vector<int> inl(n);
  for(int x:lps) inl[x]=1;
  vector<int> gr(n,-1);
  function<int(int)> dfs=[&](int v){
    if(gr[v]>=0) return gr[v];
    set<int> st;
    for(int w:g[v]) st.insert(dfs(w));
    rep(i,MOD) if(st.count(i)==0) return gr[v]=i;
  };
  rep(i,n)if(!inl[i]) dfs(i);
  auto gr_=gr;
  rep(ad,2){
    gr=gr_;
    for(int v:lps){
      int rem=(v==lps[0]?ad:0);
      set<int> st;
      for(int w:g[v])if(w!=lps.back()) st.insert(gr[w]);
      //if(v==0&&ad==1){for(int x:st) cout<<x<<",";cout<<endl;}
      rep(i,MOD)if(st.count(i)==0 && --rem<0){
	gr[v]=i;
	break;
      }
    }
    
    set<int> st;
    for(int w:g[lps[0]]) st.insert(gr[w]);
    rep(i,MOD)if(st.count(i)==0){
      if(gr[lps[0]]==i){
	cout<<"POSSIBLE"<<endl;
	//out(gr,1);
	return 0;
      }
      break;
    }
  }
  cout<<"IMPOSSIBLE"<<endl;
  return 0;
}


Measured memory_bytes: 24696