#include <iostream>
#include <cstdio>
#include <vector>
#define NMAX 100000
#define MMAX 500000
#define pii pair<int, int>
#define nod first
#define muchie second

using namespace std;

int n, m;
int uz[MMAX + 5];
vector<pii> v[NMAX + 5];

void dfs(int x, int ok) {
  pii y;

  while(!v[x].empty()) {
    y = v[x].back();
    v[x].pop_back();
    if(uz[y.muchie])
      continue;

    uz[y.muchie] = 1;
    dfs(y.nod, 0);
  }

  if(!ok)
    printf("%d ", x);
}

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

  scanf("%d %d", &n, &m);
  for(int i = 1; i <= m; i++) {
    scanf("%d %d", &x, &y);
    v[x].push_back({y, i});
    v[y].push_back({x, i});
  }

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

  dfs(1, 1);

  return 0;
}