#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 500005;
int n, m, A[nmax], B[nmax], E[nmax], viz[nmax], nrm, cnt;
vector<int>V[nmax];

void DFS(int nod)
{
    for(auto x : V[nod])
        if(viz[x] == 0)
        {
            viz[x] = 1;
            DFS(A[x] + B[x] - nod);
        }
    E[++cnt] = nod;
}
void Citire()
{
    int x, y, i;
    fin >> n >> m;
    for(i = 1;i <= m;i++)
    {
        fin >> x >> y;
        nrm++;
        A[nrm] = x;
        B[nrm] = y;
        V[x].push_back(nrm);
        V[y].push_back(nrm);
    }
}

int viz1[100005];
void Defese(int nod)
{
    viz1[nod] = 1;
    for(auto x : V[nod])
        if(viz1[x] == 0)
            Defese(x);
}
void Solve()
{
    int i;
    for(i = 1;i <= n;i++)
        if(V[i].size() % 2 == 1)
        {
            fout << "-1";
            return;
        }
    DFS(1);
    /*if(E[m] != E[1])
        fout << "-1";
    else*/
        for(i = 1;i < cnt;i++)
            fout << E[i] << " ";
}

int main()
{
    Citire();
    Solve();
    return 0;
}