#include <bits/stdc++.h>
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
const int MN = 200200;
int dp[MN];
vvi g;
bitset<MN> bs,sv,vs,sc;
vi ord,st;
bool found;
int ds(int u) {
	if(dp[u] != -1) return dp[u];
	vi ok;ok.push_back(MN+2);
	for(int i=0;i<g[u].size();i++) {
		int v = g[u][i];
		if(sc[u] && sc[v]) {continue;}
		ok.push_back(ds(v));
	}
	sort(ok.begin(),ok.end());
	int res = 0;
	while(ok[res] == res) {res++;}
	return dp[u] = res;
}
void cyc(int u) {
	st.push_back(u);
	sv.set(u);
	vs.set(u);
	for(int i=0;i<g[u].size();i++) {
		if(found) return;
		int v = g[u][i];
		if(sv[v]) {
			found = true;
			while(1) {
				ord.push_back(st.back());
				sc.set(st.back());
				if(st.back() == v) break;
				st.pop_back();
			}
			return;
		} else {
			if(!vs[v]) {
			cyc(v);
			}
		}
	}
	if(found) return;
	sv.reset(u);
	st.pop_back();
}
int n;
void calc() {
	found = false;
	for(int i=0;i<n;i++) {
		if(!vs[i]) {
			cyc(i);
		}
	}
}
int main() {
	memset(dp,-1,sizeof(dp));
	scanf("%d",&n);
	g.assign(n,vi());
	for(int i=0;i<n;i++) {
		int a;
		scanf("%d",&a);
		a--;
		g[a].push_back(i);
	}
	calc();
	int rep = ord[0];
	bool sm = true;
	for(int i=0;i<ord.size();i++) {
		if(ds(rep) != ds(ord[i])) {
			sm = false;break;
		}
	}
	bool poss = (!sm) || (ord.size()%2 == 0);
	printf("%sPOSSIBLE\n",poss?"":"IM");
}