/**
 *    author:  tourist
 *    created: 20.11.2019 07:57:53       
**/
#include <bits/stdc++.h>

using namespace std;

template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  vector<int> p(n);
  for (int i = 0; i < n; i++) {
    cin >> p[i];
    --p[i];
  }
  vector<int> deg(n);
  for (int i = 0; i < n; i++) {
    ++deg[p[i]];
  }
  vector<int> que;
  for (int i = 0; i < n; i++) {
    if (deg[i] == 0) {
      que.push_back(i);
    }
  }
  vector<set<int>> ban(n);
  vector<int> g(n, -1);
  for (int b = 0; b < (int) que.size(); b++) {
    int i = que[b];
    g[i] = 0;
    while (ban[i].find(g[i]) != ban[i].end()) {
      ++g[i];
    }
    ban[p[i]].insert(g[i]);
    --deg[p[i]];
    if (deg[p[i]] == 0) {
      que.push_back(p[i]);
    }
  }
  for (int st = 0; st < n; st++) {
    if (g[st] != -1) {
      continue;
    }
    vector<int> cycle;
    int pp = st;
    while (g[pp] == -1) {
      g[pp] = -2;
      cycle.push_back(pp);
      pp = p[pp];
    }
    int len = (int) cycle.size();
    vector<vector<int>> val(len, vector<int>(2));
    for (int i = 0; i < len; i++) {
      int x = 0;
      while (ban[cycle[i]].find(x) != ban[cycle[i]].end()) ++x;
      val[i][0] = x;
      ++x;
      while (ban[cycle[i]].find(x) != ban[cycle[i]].end()) ++x;
      val[i][1] = x;
    }
    bool found = false;
    for (int z = 0; z < 2; z++) {
      vector<vector<bool>> dp(len + 1, vector<bool>(2));
      dp[0][z] = true;
      for (int i = 1; i < len + 1; i++) {
        for (int k = 0; k < 2; k++) {
          if (dp[i - 1][k]) {
            int nj = 0;
            if (val[i % len][nj] == val[i - 1][k]) ++nj;
            dp[i][nj] = true;
          }
        }
      }
      if (dp[len][z]) {
        found = true;
        break;
      }
    }
    if (!found) {
      cout << "IMPOSSIBLE" << '\n';
      return 0;
    }
  }
  cout << "POSSIBLE" << '\n';
  return 0;
}


Measured memory_bytes: 34676