#include <bits/stdc++.h>
#define Nmax 100005
#define Mmax 500005
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int N, M;
vector<pair<int, int> > G[Nmax];
vector<int> ans;
bool vis[Mmax];

void Euler(int u) {
     while (!G[u].empty()) {
          int v = G[u].back().first;
          int edge = G[u].back().second;
          G[u].pop_back();

          if (vis[edge]) continue;
          vis[edge] = 1;
          Euler(v);
     }

     ans.push_back(u);
}
int main()
{
    fin >> N >> M;
    for (int i = 1; i <= M; ++i) {
        int x, y;
        fin >> x >> y;
        G[x].push_back({y, i});
        G[y].push_back({x, i});
    }

    for (int i = 1; i <= N; ++i)
    if (G[i].size() % 2) {
        fout << -1;
        return 0;
    }

    Euler(1);
    ans.pop_back();
    for (auto it: ans)
        fout << it << " ";


    return 0;
}