#include <bits/stdc++.h>
using namespace std;
int nxi() {
  int a;
  cin >> a;
  return a;
}
vector<int> a;
void inc(int i, int v) {
  for (; i < a.size(); i |= i + 1) {
    a[i] = max(a[i], v);
  }
}
int get(int r) {
  int ans = 0;
  for (; r >= 0; r = (r & (r + 1)) - 1) {
    ans = max(ans, a[r]);
  }
  return ans;
}
int get(int l, int r) { return get(r) - get(l - 1); }
int gcd(int a, int b) { return a == 0 ? b : gcd(b % a, a); }
const int mod = 1000000009;
int main() {
  int n = nxi();
  vector<vector<int> > adj(n);
  for (int i = 0; i < n; ++i) {
    int p = nxi();
    if (p != 0) {
      adj[p - 1].push_back(i);
      adj[i].push_back(p - 1);
    }
  }
  vector<int> dyn(n, 0);
  vector<int> answer;
  vector<int> q;
  function<void(int, int)> rec = [&](int cur, int parent) {
    int children = 0;
    int pos = 0;
    for (int v : adj[cur]) {
      if (v != parent) {
        children++;
        rec(v, cur);
        pos += dyn[v];
        if (dyn[v] == 0) {
          answer.push_back(v);
        } else {
          q.push_back(v);
        }
      }
    }
    dyn[cur] = pos % 2 == 0;
  };
  rec(0, -1);
  q.push_back(0);
  if (dyn[0]) {
    cout << "YES\n";
    for (int v : answer) cout << (v + 1) << endl;
    reverse(q.begin(), q.end());
    for (int v : q) cout << (v + 1) << endl;
  } else {
    cout << "NO\n";
  }
  return 0;
}
