#include <fstream>
#include <vector>
using namespace std;

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

vector<pair<int, int>> v[500000];
bool viz[500010];
vector<int> ccl;
int n, m;

void euler(int x)
{
    for(int i = 0; i < v[x].size(); i++)
    {
        int muchie = v[x][i].second;
        int u = v[x][i].first;
        if(!viz[muchie])
        {
            viz[muchie] = 1;
            euler(u);
        }
    }
    ccl.push_back(x);
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    bool ex = true;
    for(int i = 1; i <= n && ex; i++)
    {
        if(v[i].size() % 2 != 0)
        {
            ex = false;
        }
    }
    if(!ex)
    {
        fout << -1;
    }
    else{
        euler(1);
        for(int i = ccl.size() - 1; i >= 0; i--)
        {
            fout << ccl[i] << ' ';
        }
    }
}