#include <bits/stdc++.h>
#define MMax 500010
using namespace std;

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

int X[MMax], Y[MMax], n, m;
vector <int>L[MMax];
unsigned int P[MMax];
bool viz[MMax];
int q[MMax], K;
void Citire()
{
    int i;

    fin >> n >> m;

    for(i = 1; i <= m; i++)
    {
        fin >> X[i] >> Y[i];
        L[X[i]].push_back(i);
        L[Y[i]].push_back(i);
    }
}

inline bool Eulerian()
{
    for(int i = 1; i <= n; i++)
        if(L[i].size() % 2 == 1)
            return 0;
    return 1;
}

void DFS(int nod)
{
    int i;
    while(P[nod] < L[nod].size())
    {
        i = L[nod][P[nod]++];

        if(!viz[i])
        {
            viz[i] = 1;
            DFS(X[i] + Y[i] - nod);
        }
    }
    q[++K] = nod;
}
void Rezolva()
{

    if(!Eulerian())
        fout << "-1\n";
    else
    {
        DFS(1);

        for(int i = 1; i < K; i++)
            fout << q[i] << " ";
    }
}
int main()
{
    Citire();
    Rezolva();
    return 0;
}