#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 < 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, i = n + 1;
    if(i != n + 2)
    {
        s.push(1);
        while(s.empty() == 0)
        {
            nod = s.top();

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

                v[nod].pop_back();
            }
            else
            {
                s.pop();
                fout << nod << ' ';
            }
        }
    }

    return 0;
}