#include <fstream>
#include <vector>
#include <bitset>

using namespace std;

ifstream cin ("ciclueuler.in");
ofstream cout ("ciclueuler.out");

int n, m, x, y;

int f[100005], ind[100005];
vector <pair <int, int>> g[100005];
bitset <100005> viz;

void dfs(int nod) {
  for(; ind[nod] < g[nod].size(); ind[nod]++) {
    if(!viz[g[nod][ind[nod]].second]) {
      viz[g[nod][ind[nod]].second] = 1;
      dfs(g[nod][ind[nod]].first);
    }
  }
  if(m) {
    cout << nod << " ";
    m--;
  }
}

int main() {
  cin >> n >> m;
  for(int i = 1; i <= m; i++) {
    cin >> x >> y;
    g[x].push_back({y, i});
    g[y].push_back({x, i});
    f[x]++; f[y]++;
  }
  for(int i = 1; i <= n; i++) {
    if(f[i] % 2) {
      cout << -1;
      return 0;
    }
  }
  dfs(1);
  return 0;
}