#include <bits/stdc++.h>
#define N 500005

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

vector<pair<int, int> > v[N];
int n, m, viz[N], x, y, sol[N], k;

void Citire()
{
    int i;
    fin >> n >> m;
    for (i = 1; i <= m; i++)
    {
        fin >> x >> y;
        v[x].push_back({ y,i });
        v[y].push_back({ x,i });
    }
}


void Euler(int x)
{
    while (!v[x].empty())
    {
        int t = v[x].back().second, p = v[x].back().first;
        v[x].pop_back();
        if (viz[t] == 0)
        {
            viz[t] = 1;
            Euler(p);
        }
    }
    sol[++k] = x;
}

int main()
{
    int i;
    Citire();
    for (i = 1; i <= n; i++)
    {
        if (v[i].size() % 2 == 1) { fout << "-1"; return 0; }
    }
    Euler(1);
    for (i = 1; i < k; i++) fout << sol[i] << " ";
    return 0;
}