#include <fstream>
#include <vector>

using namespace std;

unsigned int N, M;
unsigned int u[500001], v[500001];

vector <unsigned int> L[500001];
bool seen[500001];
unsigned int pos[500001];
unsigned int K;
unsigned int i, k;

unsigned int sol[500001];

void DFS (unsigned int node)
{
    while (pos[node] < L[node].size())
    {
        K = L[node][pos[node]];
        pos[node]++;
        if (!seen[K])
        {
            seen[K] = 1;
            DFS(u[K]+v[K]-node);
        }
    }
    sol[++k] = node;
}

int main()
{
    ifstream fin ("ciclueuler.in");
    fin >> N >> M;
    for (i=1; i<=M; i++)
    {
        fin >> u[i] >> v[i];
        L[u[i]].push_back(i);
        L[v[i]].push_back(i);
    }
    ofstream fout("ciclueuler.out");
    for (i=1; i<=N; i++)
        if (L[i].size()%2 == 1)
        {
            fout << -1;
            return 0;
        }
    DFS(1);
    for (i=1; i<k; i++)
        fout << sol[i] << ' ';
    fout.close();
    return 0;
}