#include <bits/stdc++.h>
using namespace std;
vector<int> D[200000], T;
int S[200000];
void dfsS(int d, int p) {
  S[d] = 1;
  for (int i = 0; i < D[d].size(); i++) {
    if (D[d][i] != p) {
      dfsS(D[d][i], d);
      S[d] += S[D[d][i]];
    }
  }
  return;
}
void dfs(int d, int p) {
  int A;
  for (int i = 0; i < D[d].size(); i++) {
    A = D[d][i];
    if (A != p && S[A] % 2 == 0) {
      dfs(A, d);
    }
  }
  cout << d + 1 << "\n";
  for (int i = 0; i < D[d].size(); i++) {
    A = D[d][i];
    if (A != p && S[A] % 2 == 1) {
      dfs(A, d);
    }
  }
  return;
}
int main() {
  ios::sync_with_stdio(false);
  int n, a;
  cin >> n;
  if (n % 2 == 0) {
    cout << "NO";
    return 0;
  }
  cout << "YES"
       << "\n";
  for (int i = 0; i < n; i++) {
    cin >> a;
    if (a != 0) {
      a--;
      D[a].push_back(i);
      D[i].push_back(a);
    }
    S[i] = 0;
  }
  T.push_back(0);
  dfsS(0, 0);
  dfs(0, -1);
  return 0;
}
