#include <cstdio>
#include <cstdlib>
#include <vector>
#include <stack>
#include <bitset>
using namespace std;

const int MAXM = 500005;
const int MAXN = 100005;

int n, m;

struct M{
  int x, y;
  bool removed;
  M() : removed(0) { }
};

vector<M> muchii;
vector<int> graf[MAXN];
stack<int> st;

int main() {
  freopen("ciclueuler.in", "r", stdin);
  freopen("ciclueuler.out", "w", stdout);

  scanf("%d %d ", &n, &m);

  M k;
  for (int i = 0; i < m; i++) {
    scanf("%d %d ", &k.x, &k.y);
    muchii.push_back(k);
    graf[k.x].push_back(i);
    graf[k.y].push_back(i);
  }

  for (int i = 1; i <= n; i++)
    if (graf[i].size() % 2) {
      printf("-1\n");
      exit(0);
    }

  st.push(1);

  while (!st.empty()) {
    int x = st.top();

    if (!graf[x].empty()) {
      int it = graf[x].front();
      graf[x].erase(graf[x].begin(), graf[x].begin() + 1);

      if(!muchii[it].removed) {
        muchii[it].removed = 1;
        int toAdd = x != muchii[it].x ? muchii[it].x : muchii[it].y;
        st.push(toAdd);
        continue;
      }
    } else {
      st.pop();
      printf("%d ", x);
    }
  }

  return 0;
}