#include <bits/stdc++.h>

using namespace std;

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

const int DIM=1e5+5;

int n,m;
vector<pair<int,int>> v[DIM];
vector<int> solutie;
bool used[5*DIM];

void euler(int nod)
{
    while(!v[nod].empty())
    {
        pair<int,int> e=v[nod].back();
        v[nod].pop_back();
        if (used[e.second])
            continue;
        used[e.second]=true;
        euler(e.first);
    }
    solutie.push_back(nod);
}

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

    bool admite = true;
    for (int i = 1;i <=n ;i++){
        if (int(v[i].size())%2==1)
        {
            admite=false;
            break;
        }
    }

    if (!admite){
        g<<-1;
        exit(0);
    }
    euler(1);

    solutie.pop_back();
    for (auto it : solutie)
        g<<it<<" ";

    return 0;
}