#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define pf push_front
#define MOD 1000000007
#define MAX 100005

using namespace std;

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

vector < int > answer;
vector < pair < int, int> > v[MAX];
stack < int > s;
bitset < 5 * MAX > viz;

int main()
{
    int n, m, x, y, i, nod;

    fin >> n >> m;
    for(i = 1; i <= m; ++i)
    {
        fin >> 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)
        {
            fout << -1;
            return 0;
        }

    s.push(1);
    while(s.empty() == 0)
    {
        nod = s.top();
        int im = v[nod][v[nod].size() - 1].second;

        if(v[nod].size())
        {
            if(viz[im] == 0)
            {
                viz[im] = 1;
                s.push(v[nod][v[nod].size() - 1].first);
            }

            v[nod].pop_back();
        }
        else
        {
            s.pop();
            answer.push_back(nod);
        }
    }
    answer.pop_back();
    for(int i = 0; i <= answer.size() - 1; ++i)
        fout << answer[i] << " ";
    return 0;
}