#include <bits/stdc++.h>

#define N 100005
#define M 500005

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n, m;
vector<pair<int, int>> graf[N];
stack<int> s;
vector<int> result;
bool viz[M];


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

void solve() {
  for(int i = 1;i <= n;++i) {
    if(graf[i].size() % 2) {
      g<<-1;
      return;
    }
  }

  s.push(1);

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

    if(graf[top].size()) {
      auto back = graf[top].back();
      if(!viz[back.second]) {
        s.push(back.first);
      }
      viz[back.second] = true;
      graf[top].pop_back();
    } else {
      s.pop();
      result.push_back(top);
    }
  }
  for(const auto& el : result) {
    g<<el<<" ";
  }
}


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