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

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

int n,m,grad[nmax];
bool sters[nmax*5];

struct str
{
    int nod,indice;
};
vector<int>V;
vector<str>Q[nmax];
vector<int>edges;

void solve()
{
    int indic=1;
    while (!Q[indic].size())
    {
        ++indic;
    }
    V.push_back(indic);
    while (!V.empty())
    {
        int nod=V.back();
        while (Q[nod].size()&&sters[Q[nod].back().indice])
        {
            Q[nod].pop_back();
        }
        if (Q[nod].size())
        {
            sters[Q[nod].back().indice]=true;
            V.push_back(Q[nod].back().nod);
        }
        else
        {
            edges.push_back(nod);
            V.pop_back();
        }
    }
    int sz=edges.size()-1;
    for (int i=0; i<sz; ++i)
        g<<edges[i]<<' ';
}

void read()
{
    f>>n>>m;
    for (int i=1; i<=m; ++i)
    {
        int h1,h2;
        f>>h1>>h2;
        Q[h1].push_back({h2,i});
        Q[h2].push_back({h1,i});
        ++grad[h1];
        ++grad[h2];
    }
}
int main()
{
    read();
    bool grades=true;
    for (int i=1; i<=n; ++i)
        if (grad[i]%2!=0)
            grades=false;
    if (grades==true)
        solve();
    else
        g<<-1;
    return 0;
}