// need
#include <iostream>
#include <algorithm>

// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <array>
#include <unordered_map>

// stream
//#include <istream>
//#include <sstream>
//#include <ostream>
#include <fstream>

// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest&...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int i=0; i<n; ++i){MACRO_VEC_ROW_Scan(i, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest&...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest&...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& r:c)for(auto& i:r)std::cin>>i;

// output
#define OUT(d) std::cout<<(d);
#define FOUT(n, d) std::cout<<std::fixed<<std::setprecision(n)<<(d);
#define SOUT(n, c, d) std::cout<<std::setw(n)<<std::setfill(c)<<(d);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(i, n) std::cout<<(i + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(d) {std::cerr << #d << "\t:" << (d) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}

// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i)
#define REP(i, n) for(int i=0;i<int(n);++i)
#define RREP(i, n) for(int i=int(n)-1;i>=0;--i)
#define FORLL(i, a, b) for(ll i=ll(a);i<ll(b);++i)
#define RFORLL(i, a, b) for(ll i=ll(b)-1;i>=ll(a);--i)
#define REPLL(i, n) for(ll i=0;i<ll(n);++i)
#define RREPLL(i, n) for(ll i=ll(n)-1;i>=0;--i)
#define IN(a, x, b) (a<=x && x<b)
template<typename T> inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; }
template<typename T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
#define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]"
#define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;}
void CHECKTIME(std::function<void()> f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start)).count(); std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n"; }

// test
template<class T> std::vector<std::vector<T>> VV(int n, int m, T init = T()) {
	return std::vector<std::vector<T>>(n, std::vector<T>(m, init));
}
template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

// type/const
//#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = 1 << 30;                          // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-9;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;

template<class T, size_t N> void FILL(T(&a)[N], const T& val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T& val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T>& a, const T& val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>>& a, const T& val) { for (auto& b : a) FILL(b, val); }

// ------------>8------------------------------------->8------------



signed main() {
	INIT;

	VAR(int, n);
	VEC(int, p, n);

	std::vector<std::vector<int>> g(n), g2(n);
	std::vector<int> in(n, 0), in2(n, 0);
	REP(i, n) {
		--p[i];
		g[p[i]].emplace_back(i);
		g2[i].emplace_back(p[i]);
		++in[i];
		++in2[p[i]];
	}

	std::vector<int> ord(n, -1);
	int LIM;
	{
		std::queue<int> que;
		REP(i, n) if (in[i] == 0) que.push(i);
		int p = 0;
		while (!que.empty()) {
			int now = que.front(); que.pop();
			ord[now] = p++;
			for (int to : g[now]) {
				if (--in[to] == 0) {
					que.push(to);
				}
			}
		}
		if (p == n) {
			OUT("POSSIBLE")BR;
			return 0;
		}
		LIM = p;
	}
	{
		std::queue<int> que;
		REP(i, n) if (in2[i] == 0) que.push(i);
		int p = n - 1;
		while (!que.empty()) {
			int now = que.front(); que.pop();
			ord[now] = p--;
			for (int to : g2[now]) {
				if (--in2[to] == 0) {
					que.push(to);
				}
			}
		}
	}

	std::set<int> cycle;
	REP(i, n) if (ord[i] == -1) cycle.insert(i);

	if (cycle.size() % 2 == 0) {
		OUT("POSSIBLE")BR;
		return 0;
	}

	std::vector<int> grundy(n, -1);
	std::vector<int> v;
	REP(i, n) if (ord[i] > LIM) v.emplace_back(i);
	std::sort(ALL(v), [&](int l, int r) { return ord[l] > ord[r]; });

	auto getGrundy = [&](int x) {
		int res = 0;
		std::set<int> set;
		for (auto& to : g[x]) set.insert(grundy[to]);
		while (set.count(res)) ++res;
		return res;
	};

	REP(i, v.size()) {
		int now = v[i];
		grundy[now] = getGrundy(now);
	}

	int base = *cycle.begin();
	{
		grundy[base] = getGrundy(base);
		int now = base;
		while (true) {
			for (auto& to : g2[now]) {
				if (cycle.count(to)) {
					now = to;
					break;
				}
			}
			if (now == base) break;
			grundy[now] = getGrundy(now);
		}
		if (grundy[base] == getGrundy(base)) {
			OUT("POSSIBLE")BR;
			return 0;
		}
	}
	for (auto& x : cycle) grundy[x] = -1;
	/////////////////////////////////////////////////////////////////////////

	{
		grundy[base] = getGrundy(base);
		int baseto = -1;
		for (auto& to : g[base]) {
			if (cycle.count(to)) {
				baseto = to;
				break;
			}
		}
		grundy[baseto] = grundy[base];
		grundy[base] = getGrundy(base);

		int now = base;
		while (true) {
			for (auto& to : g2[now]) {
				if (cycle.count(to)) {
					now = to;
					break;
				}
			}
			if (now == baseto) break;
			grundy[now] = getGrundy(now);
		}
		if (grundy[baseto] == getGrundy(baseto)) {
			OUT("POSSIBLE")BR;
			return 0;
		}
	}
	OUT("IMPOSSIBLE")BR;
	return 0;
}

Measured memory_bytes: 31744