#include <bits/stdc++.h>
using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");

const int nmax = 100006, mmax = 500006;
int n, m, poz[mmax];
vector <pair <int, int>> vecini[nmax];
vector<int> vrasp;

void dfs(int x)
{
    while(vecini[x].size()!=0)
    {
        int vec, nr_muchie;
        tie(vec, nr_muchie) = vecini[x].back();
        vecini[x].pop_back();

        if(poz[nr_muchie]==0)
        {
            poz[nr_muchie] = 1;
            dfs(vec);
        }
    }

    vrasp.push_back(x);
}

int main()
{
    in>>n>>m;
    for(int i = 0; i<m; i++)
    {
        int a, b;
        in>>a>>b;

        vecini[a].push_back(make_pair(b, i));
        vecini[b].push_back(make_pair(a, i));
    }

    for(int i = 1; i<=n; i++)
    {
        if(vecini[i].size()%2==1)
        {
            out<<"-1\n";
            return 0;
        }
    }

    dfs(1);

    for(int i = 0; i<(int)vrasp.size() - 1; i++)
    {
        out<<vrasp[i]<<' ';
    }


    return 0;
}