#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].pb({y, i});
        v[y].pb({x, i});
    }

    for(i = 1; i <= n; i++) if(v[i].size() % 2 == 1) fout << -1, i = n + 2;

    if(i != n + 3)
    {
        s.push(1);
        while(s.empty() == 0)
        {
            nod = s.top();
            x = v[nod][v[nod].size() - 1].first, y = v[nod][v[nod].size() - 1].second;

            if(v[nod].empty() == 0)
            {
                if(viz[y] == 0) viz[y] = 1, s.push(x);
                v[nod].pop_back();
            }
            else
            {
                s.pop();
                if(s.empty() == 0) fout << nod << ' ';
            }
        }
    }

    return 0;
}