#include <bits/stdc++.h>
#define N 100005
#define M 500100
using namespace std;

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

int A[M], B[M], n, m;
vector <int> h[N];
vector <int> l[N];
bitset <M> viz;
int g[N];
int E[M], k;

void Read()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        fin >> A[i] >> B[i];
        h[A[i]].push_back(i);
        h[B[i]].push_back(i);
        l[A[i]].push_back(B[i]);
        l[B[i]].push_back(A[i]);
        g[A[i]]++;
        g[B[i]]++;
    }
}
void DFS(int sNode)
{
    viz[sNode] = 1;
    for(auto i : l[sNode])
        if(viz[i] == 0)
            DFS(i);
}

int IsEuler()
{
    DFS(A[1]);
    for(int i = 1; i <= n; i++)
    {
        if(g[i] % 2 == 1) return 0;
        if(g[i] > 0 && viz[i] == 0) return 0;
    }
    return 1;
}
void Euler(int sNode)
{
    for(auto i : h[sNode])
        if(viz[i] == 0)
        {
            viz[i] = 1;
            Euler(A[i] + B[i] - sNode);
        }
    E[++k] = sNode;
}
int main()
{
    Read();
    if(IsEuler() == 0)
    {
        fout << "-1\n";
        return 0;
    }
    viz.reset();
    Euler(A[1]);
    for(int i = 1; i < k; i++)
        fout << E[i] << " ";
    return 0;
}