#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define M 200020
using namespace std;
int read(){
	int nm=0,fh=1; char cw=getchar();
	for(;!isdigit(cw);cw=getchar()) if(cw=='-') fh=-fh;
	for(;isdigit(cw);cw=getchar()) nm=nm*10+(cw-'0');
	return nm*fh;
}
int n,m,fs[M],nt[M],to[M],fa[M],tmp,cnt,Mx,Mn,v[M];
bool vis[M],lp[M],hv[M];
void link(int x,int y){nt[tmp]=fs[x],fs[x]=tmp,to[tmp++]=y;}
void dfs(int x){
	for(int i=fs[x];i!=-1;i=nt[i]) if(!lp[to[i]]) dfs(to[i]);
	for(int i=fs[x];i!=-1;i=nt[i]) if(!lp[to[i]]) hv[v[to[i]]]=true;
	while(hv[v[x]]) v[x]++;
	for(int i=fs[x];i!=-1;i=nt[i]) if(!lp[to[i]]) hv[v[to[i]]]=false;
}
int main(){
	n=read(),memset(fs,-1,sizeof(fs)),Mn=n+1;
	for(int i=1;i<=n;i++) fa[i]=read(),link(fa[i],i);
	for(m=1;!vis[m];m=fa[m]) vis[m]=true;
	for(;!lp[m];m=fa[m]) cnt++,lp[m]=true;
	for(m=1;m<=n;m++) if(lp[m]) dfs(m),Mx=max(Mx,v[m]),Mn=min(Mn,v[m]);
	puts((cnt&1)&&Mx==Mn?"IMPOSSIBLE":"POSSIBLE"); return 0;
}