#include <iostream>
#include<fstream>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#define dim 100002
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n,m,viz[100002];
vector< vector<int> >a;
queue<int>q;
stack<int>st;
void citire()
{
    f>>n>>m;
    a=vector< vector<int> >(n+1);
    for(int i=1;i<=m;i++)
    {
        int x,y;
        f>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);
    }
}
void bfs(int i)
{
    viz[i]=1;
    q.push(i);
    while(!q.empty())
    {
        int x=q.front();
        for(vector<int>::iterator it=a[x].begin();it!=a[x].end();it++)
        {
            if(viz[*it]==0)
            {
                q.push(*it);
                viz[*it]=1;
            }
        }
        q.pop();
    }
}
int verifica()
{
    int y=1;
    bfs(1);
    for(int i=1;i<=n;i++)
    if(viz[i]==0 or a[i].size()%2==1)
    {
        y=0;
        break;
    }
    return y;
}
void ciclu_euler(int nod)
{
    int v,vf;
    st.push(nod);
    while(!st.empty())
    {
        v=st.top();
        if(a[v].size()!=0)
        {
            vf=a[v].back();
            a[v].pop_back();
            a[vf].erase(find(a[vf].begin(),a[vf].end(),v));
            st.push(vf);
        }
        else
        {
            if(!st.empty()) g<<v<<" ";
            st.pop();

        }
    }
}
int main()
{
    citire();
    int x=verifica();
    if(x==0) g<<"-1";
    else
    ciclu_euler(1);
    g<<"\n";
    return 0;
}