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

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

int A[5*N], B[5*N], d[N], v[5*N], e[5*N], len, n, m;
vector <int> L[N];

void DFS(int k)
{
    for (int i : L[k])
    {
        if (v[i]) continue;
        v[i] = 1;
        DFS(A[i] + B[i] - k);
    }
    e[++len] = k;
}

int main()
{
    int i, j;
    fin >> n >> m;
    for (int p = 1; p <= m; p++)
    {
        fin >> i >> j;
        d[i]++;
        d[j]++;
        A[p] = i;
        B[p] = j;
        L[i].push_back(p);
        L[j].push_back(p);
    }

    for (i = 1; i <= n; i++)
        if (d[i] % 2 != 0)
        {
            fout << "-1\n";
            return 0;
        }

    DFS(1);
    for (i = 1; i < len; i++)
        fout << e[i] << " ";
    return 0;
}