#include <bits/stdc++.h>
#define oo 0x3f3f3f3f
#define edge pair<int, int>
#define number first
#define node second

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n, m;
vector<edge> graf[100001];
vector<int> result;
bool eliminat[500001];

void read()
{
  f>>n>>m;
  int x, y;
  
  for(int i = 1;i <= m;++i)
    f>>x>>y, graf[x].push_back(make_pair(i, y)), graf[y].push_back(make_pair(i, x));
}

void solve()
{
  for(int i = 1;i <= n;++i)
    if(graf[i].size() & 1)
    {
      g<<-1;
      return;
    }

  stack<int> s;
  s.push(1);

  while(!s.empty())
  {
    int node_f = s.top();

    if(!graf[node_f].empty())
    {
      edge e = graf[node_f].back();
      graf[node_f].pop_back();

      if(!eliminat[e.number])
      {
        eliminat[e.number] = true;
        s.push(e.node);
      }
    }
    else
    {
      s.pop();
      result.push_back(node_f);
    }
  }
  
  for(auto it : result)
    g<<it<<" ";
}


int main()
{
  read();
  solve();
  return 0;
}