#include <bits/stdc++.h>
using namespace std;
const int inf = 1000000000;
long long mod = 1000000009LL;
long long mod2 = 998244353LL;
int t;
int n;
int p[200005];
int deg[200005];
int deg2[200005];
vector<int> edges[200005];
int main() {
  cin >> n;
  vector<int> ans(n, 0);
  int l = 0, r = n - 1;
  memset(deg, 0, sizeof(deg));
  memset(deg2, 0, sizeof(deg2));
  for (int i = 1; i <= n; ++i) {
    scanf("%d", &p[i]);
    if (p[i] == 0) continue;
    edges[p[i]].push_back(i);
    edges[i].push_back(p[i]);
    deg[i]++;
    deg[p[i]]++;
    deg2[i]++;
    deg2[p[i]]++;
  }
  if (n == 1) {
    cout << "YES" << endl;
    cout << 1 << endl;
    return 0;
  }
  if (n % 2 == 0) {
    cout << "NO" << endl;
    return 0;
  }
  queue<int> q;
  for (int i = 1; i <= n; ++i) {
    if (deg[i] == 1) {
      q.push(i);
    }
  }
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    if (deg[u] % 2) {
      ans[r--] = u;
    } else {
      ans[l++] = u;
      for (int i = 0; i < edges[u].size(); ++i) {
        int v = edges[u][i];
        deg[v]--;
      }
    }
    for (int i = 0; i < edges[u].size(); ++i) {
      int v = edges[u][i];
      deg2[v]--;
      if (deg2[v] == 1) {
        q.push(v);
      }
    }
  }
  if (l > r) {
    cout << "YES" << endl;
    for (int i = 0; i < ans.size(); ++i) {
      printf("%d\n", ans[i]);
    }
  } else {
    cout << "NO" << endl;
  }
  return 0;
}
