#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  map<long long, vector<long long> > m;
  map<long long, bool> v;
  map<long long, long long> c;
  vector<long long> b;
  long long i, j, k, x, y, r;
  for (i = 1; i <= n; i++) {
    cin >> x >> y;
    if (x == -1)
      r = i;
    else
      m[x].push_back(i);
    v[i] = false;
    c[i] = y;
  }
  for (i = 1; i <= n; i++) {
  }
  queue<long long> q;
  q.push(r);
  long long f = 1;
  while (!q.empty()) {
    j = q.front();
    if (c[j] == 1) f = 0;
    for (i = 0; i < m[j].size(); i++) {
      q.push(m[j][i]);
      if (c[m[j][i]] != 1 and !f) {
        f = 1;
      }
    }
    if (f == 0) {
      b.push_back(j);
    }
    f = 1;
    q.pop();
  }
  if (b.size() == 0)
    cout << -1;
  else {
    sort(b.begin(), b.begin() + b.size());
    for (i = 0; i < b.size(); i++) {
      cout << b[i] << " ";
    }
  }
}
