#include <fstream>
#include <vector>

using namespace std;

void DFS (unsigned int node);

unsigned int N, M;
unsigned int u[500005], v[500005];

vector <unsigned int> L[500005];
bool seen[500005];
unsigned int pos[500005];
unsigned int k, K;
unsigned int i;

unsigned int sol[500005];

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);
    }
    fin.close();
    ofstream fout ("ciclueuler.out");
    for (i=1; i<=N; i++)
        if (L[i].size()%2 != 0)
        {
            fout << -1;
            return 0;
        }
    DFS(1);
    for (i=1; i<K; i++)
        fout << sol[i] << ' ';
    fout.close();
    return 0;
}

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