#include <bits/stdc++.h>
#define N 100004
#define M 500100
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int A[M] , B[M] , d[N] , E[M] , k;
bitset <M> viz;
unsigned ind[N];
int n , m;
vector <int> L[M];
vector <int> H[M];
void Citire()
{
    int i;
    fin >> n >> m;
    for(i = 1; i <= m; i++)
    {
        fin >> A[i] >> B[i];
        L[A[i]].push_back(i);
        L[B[i]].push_back(i);
        H[A[i]].push_back(B[i]);
        H[B[i]].push_back(A[i]);
        d[A[i]]++;
        d[B[i]]++;
    }
    fin.close();
}
void DFS(int nod)
{
    viz[nod] = 1;
    for(auto j : H[nod])
        if(viz[j] == 0)
            DFS(j);
}
int EsteEuler()
{
    int i;
    ///este euler daca gradele sunt pare si este conex
    DFS(A[1]);
    for(i = 1; i <= n; i++)
    {
        if(d[i] % 2 != 0)return 0;
        if(d[i] > 0 && viz[i] == 0)return 0;
    }
    return 1;
}

void Euler(int nod)
{
    while (ind[nod] < L[nod].size())
    {
        int i = L[nod][ind[nod]++];
        if (viz[i] == 0)
        {
            viz[i] = 1;
            Euler(A[i] + B[i] - nod);
        }
    }
    E[++k] = nod;
}
int main()
{
    Citire();
    if(!EsteEuler())
    {
        fout << "-1\n";
        fout.close();
        return 0;
    }
    viz.reset();
    Euler(A[1]);
    for(int i = 1; i < k; i++)
        fout << E[i] << " ";
    return 0;
}