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

vector<int> G[100002];
stack<int> st;
int viz[100002];
int n,m,i,j,x,y, grad;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

void parc_adancime(int plecare) {
    viz[plecare] = 1;
    int i;
    for (i=0;i<G[plecare].size();i++)
        if (viz[G[plecare][i]] == 0)
            parc_adancime(G[plecare][i]);
}

void stergeMuchia(int varf, int last)   {
    int i;
    /*for (i=G[varf].begin();i<G[varf].end();i++) {
        if (i == last)
            G[varf].erase(i);
    }*/
   for (vector<int>::iterator it = G[varf].begin(); it != G[varf].end(); it++)
        if (*it == last)
        {
            G[varf].erase(it);
            return;
        }
}
int main()
{
    f>>n>>m;
    for (i=1;i<=m;i++)  {
        f>>x>>y;
        G[x].push_back(y);
        G[y].push_back(x);
    }
    parc_adancime(1);
    for (i=1;i<=n;i++)  {
        grad = G[i].size();
        if (viz[i]==0 || grad % 2 !=0)
            g<<-1;
    }
    st.push(1);//adaug elementu 1 in stiva
    while ( !st.empty() )   {
        int varf = st.top();//Varf stiva
        int gradVarf = G[varf].size();
        if (gradVarf == 0)  {
            st.pop();
            if ( !st.empty() )
                g<<varf<<"\t";
        }
        else    {
            int last = G[varf].back();
            G[varf].pop_back();
            stergeMuchia(last, varf);
            st.push(last);
        }
    }

    return 0;
}