#include <bits/stdc++.h>
#define ADD(a, b) a = (a + ll(b)) % mod
#define MUL(a, b) a = (a * ll(b)) % mod
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)
#define rep(i, a, b) for(int i = int(a); i < int(b); i++)
#define rer(i, a, b) for(int i = int(a) - 1; i >= int(b); i--)
#define all(a) (a).begin(), (a).end()
#define sz(v) (int)(v).size()
#define pb push_back
#define sec second
#define fst first
#define debug(fmt, ...) Debug(__LINE__, ":", fmt, ##__VA_ARGS__)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<int, pi> ppi;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> mat;
typedef complex<double> comp;
void Debug() {cout << '\n'; }
template<class FIRST, class... REST>void Debug(FIRST arg, REST... rest){
	cout<<arg<<" ";Debug(rest...);}
template<class T>ostream& operator<<(ostream& out,const vector<T>& v) {
	out<<"[";if(!v.empty()){rep(i,0,sz(v)-1)out<<v[i]<<", ";out<<v.back();}out<<"]";return out;}
template<class S, class T>ostream& operator<<(ostream& out,const pair<S, T>& v){
	out<<"("<<v.first<<", "<<v.second<<")";return out;}
const int MAX_N = 200010;
const int MAX_V = 100010;
const double eps = 1e-6;
const ll mod = 1000000007;
const int inf = 1 << 29;
const ll linf = 1LL << 60;
const double PI = 3.14159265358979323846;
///////////////////////////////////////////////////////////////////////////////////////////////////

int N, M;
vector<int> G[MAX_N], rG[MAX_N];
int cnt[MAX_N];
int p[MAX_N];
bool dp[MAX_N][2];
int grundy[MAX_N];
int d[MAX_N];
bool used[MAX_N];
int nex[MAX_N];
vector<int> vec; //loop

int loop(int v, int ng) {
	set<int> S;
	int res = 0;
	rep(i, 0, sz(G[v])) {
		int n = G[v][i];
		if(n == ng) continue;
		S.insert(loop(n, -1));
	}
	for(int s : S) {
		if(s == res) res++;
		else return res;
	}
	return res;
}

void solve() {
	cin >> N;
	rep(i, 0, N) {
		int a; cin >> a; a--;
		G[a].pb(i);
		rG[i].pb(a);
		cnt[a]++;
	}
	queue<int> que;
	rep(i, 0, N) {
		if(cnt[i] == 0) que.push(i);
	}
	while(!que.empty()) {
		int v = que.front(); que.pop();
		used[v] = true;
		rep(i, 0, sz(rG[v])) {
			int n = rG[v][i];
			cnt[n]--;
			if(cnt[n] == 0) {
				que.push(n);
			}
		}
	}
	rep(i, 0, N) if(!used[i]) vec.pb(i);
	M = sz(vec);
	int v = vec[0];
	rep(i, 0, M) {
		int tnex = -1;
		rep(i, 0, sz(G[v])) {
			int n = G[v][i];
			int tat = lower_bound(all(vec), n) - vec.begin();
			if(tat != M && vec[tat] == n) {
				tnex = n;
			}
		}
		grundy[i] = loop(v, tnex);
		v = tnex;
	}

	rep(q, 0, 2) {
		memset(dp, 0, sizeof(dp));
		dp[0][q]= true;
		rep(i, 0, M) {
			rep(j, 0, 2) {
				if(!dp[i][j]) continue;
				int nid = (i + 1) % M;
				if(j == 0) {
					if(grundy[nid] != grundy[i]) {
						dp[i + 1][0] = true;
					}
					if(grundy[nid] + 1 != grundy[i]) {
						dp[i + 1][1] = true;
					}
				}
				else {
					if(grundy[nid] == (grundy[i] + 1) - 1) {
						dp[i + 1][0] = true;
					}
					if(grundy[nid] + 1 == (grundy[i] + 1) - 1) {
						dp[i + 1][1] = true;
					}
				}
			}
		}
		if(dp[M][q]) {
			cout << "POSSIBLE\n";
			return;
		}
	}
	cout << "IMPOSSIBLE\n";
}

int main() {
#ifndef LOCAL
	ios::sync_with_stdio(false);
    cin.tie(0);
#endif
    cout << fixed;
	cout.precision(20);
	srand((unsigned int)time(NULL));
#ifdef LOCAL
	//freopen("in.txt", "wt", stdout); //for tester
    freopen("in.txt", "rt", stdin);
#endif	
	solve();
#ifdef LOCAL
    cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
	return 0;
}



Measured memory_bytes: 24952