#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

vector <int> G[100010];
vector <int> stk;
vector <int> ans;
int from[500100],to[500100],n,m;
bool viz[500100];

int main()
{
    f>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int a,b;
        f>>a>>b;
        G[a].push_back(i);
        G[b].push_back(i);
        from[i]=a;
        to[i]=b;
    }
    f.close();
    for(int i=1;i<=n;i++)
        if(G[i].size()%2==1)
            {
                g<<-1;
                g.close();
                return 0;
            }
    stk.push_back(1);
    while(!stk.empty())
    {
        int nod=stk.back();
        if(!G[nod].empty())
        {
            int muchie=G[nod].back();
            G[nod].pop_back();
            if(!viz[muchie])
            {
                viz[muchie]=1;
                if(nod==from[muchie])
                    stk.push_back(to[muchie]);
                else stk.push_back(from[muchie]);
            }
        }
        else
        {
            stk.pop_back();
            ans.push_back(nod);
        }
    }
    for(int i=0;i<ans.size()-1;i++)
        g<<ans[i]<<' ';
    g.close();
    return 0;
}