#include <bits/stdc++.h>
using namespace std;
int n;
basic_string<int> e[200005];
bool sa[200005], bez[200005];
void dfs1(int x, int p) {
  bool lose = false;
  int bravo = -1;
  int csa = 0, cbez = 0;
  for (int y : e[x]) {
    if (y != p) {
      dfs1(y, x);
      if (!sa[y] && !bez[y]) {
        lose = true;
      } else if (sa[y] && bez[y]) {
        bravo = y;
      } else if (sa[y]) {
        csa++;
      } else {
        cbez++;
      }
    }
  }
  if (lose) {
    sa[x] = bez[x] = false;
    return;
  }
  if (bravo == -1) {
    if (cbez % 2) {
      sa[x] = true;
      bez[x] = false;
    } else {
      sa[x] = false;
      bez[x] = true;
    }
  } else {
    sa[x] = bez[x] = true;
  }
}
void dfs2(int x, int p, bool gore) {
  basic_string<int> lsa, lbez, lbravo;
  for (int y : e[x]) {
    if (y != p) {
      if (!sa[y] && !bez[y]) {
      } else if (sa[y] && bez[y]) {
        lbravo += y;
      } else if (sa[y]) {
        lsa += y;
      } else {
        lbez += y;
      }
    }
  }
  for (int y : lsa) {
    dfs2(y, x, true);
  }
  while (gore ^ ((lbez.size() + lbravo.size()) % 2 == 1)) {
    dfs2(lbravo.back(), x, true);
    lbravo.pop_back();
  }
  cout << x << '\n';
  for (int y : lbravo) dfs2(y, x, false);
  for (int y : lbez) dfs2(y, x, false);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cerr.tie(nullptr);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    int x;
    cin >> x;
    if (x) {
      e[i] += x;
      e[x] += i;
    }
  }
  dfs1(1, 1);
  if (!bez[1]) {
    cout << "NO\n";
    return 0;
  }
  cout << "YES\n";
  dfs2(1, 1, false);
}
