#include <iostream>
#include <fstream>
#include <vector>
#define Nmax 100005

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n, m, x, y;
vector <pair <int, int> > v[Nmax];
vector <int > sol;
bool seen[5*Nmax];

bool verif()
{
    for (int i = 1; i <= n; i++)
        if(v[i].size()%2 == 1) return 0;

    return 1;
}

void euler(int x)
{
    while(!v[x].empty())
    {
        int y=v[x].back().first;
        int muchie=v[x].back().second;
        v[x].pop_back();
        if(seen[muchie] == 1) continue;

        seen[muchie]=1;
        euler(y);
    }
    sol.push_back(x);
}

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

    if(verif() == 0)
    {
        g << "-1\n";
        return 0;
    }

    euler(1);
    sol.pop_back();
    for (auto i:sol)
        g << i << " ";

    return 0;
}