#include <bits/stdc++.h>
using namespace std;
const int Inf = (int)1e9;
const long long InfL = (long long)1e18;
const int MaxN = (int)2e5 + 5;
vector<int> adj[MaxN], ans;
int n, a, deg[MaxN], dead[MaxN];
void dfs2(int x, int p) {
  dead[x] = true;
  ans.push_back(x);
  for (auto u : adj[x]) --deg[u];
  for (auto u : adj[x])
    if (u != p && !dead[u]) dfs2(u, x);
}
void dfs1(int x, int p) {
  for (auto u : adj[x])
    if (u != p) dfs1(u, x);
  if (!(deg[x] & 1)) dfs2(x, p);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a;
    if (!a) continue;
    adj[i].push_back(a);
    deg[i]++;
    adj[a].push_back(i);
    deg[a]++;
  }
  dfs1(1, 0);
  if (ans.size() == n) {
    cout << "YES" << '\n';
    for (int i = 0; i < n; i++) cout << ans[i] << '\n';
  } else {
    cout << "NO" << '\n';
  }
  return 0;
}
