#include <iostream>
#include <stack>
#include <fstream>
#include <queue>
#include <vector>
#include <bitset>
#include <algorithm>
using namespace std;
int n,m,grad[100005];
vector <int> v[100005];
bitset <100005> apar;
fstream f,g;
void bfs (int vf)
{
    queue<int> q;
    q.push(vf);
    apar[vf]=1;
    int i;
    while (!q.empty())
    {
        vf=q.front();
        q.pop();
        for (i=0;i<v[vf].size();i++)
            if (apar[v[vf][i]]==0)
                {
                    q.push(v[vf][i]);
                    apar[v[vf][i]]=1;
                }
    }

}

void euler (int vf)
{
    int i,vfcrt;
    stack <int> st;
    st.push(vf);
    while (!st.empty())
    {
        vf=st.top();
        //st.pop();
        if(v[vf].size()==0)
           {
               st.pop();
                if (!st.empty())
                g<<vf<<" ";
           }
        else
        {
            for (i=0;i<v[vf].size();i++)
            {
                vfcrt=v[vf][i];
                v[vf].erase(find(v[vf].begin(),v[vf].end(),vfcrt));
                v[vfcrt].erase(find(v[vfcrt].begin(),v[vfcrt].end(),vf));
                st.push(vfcrt);
                break;
            }
        }
    }

}
int main()
{
    int i,x,y;
    f.open("ciclueuler.in",ios::in);
    g.open("ciclueuler.out",ios::out);
    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y;
        grad[x]++;
        grad[y]++;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    bfs(1);
   for(i=1;i<=n;i++)
        if (apar[i]==0 || grad[i]%2==1)
        {
            g<<-1;
            return 0;
        }
     for(i=1;i<=n;i++)
        if (apar[i]==0)
        {
            g<<-1;
            return 0;
        }
    euler(1);
}