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

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m, a[500001],k;
bool viz[500001];
vector <pair<int,int> > v[100002];

void euler(int nod)
{
    while(!v[nod].empty())
    {
        int p = v[nod].back().second;
        int next = v[nod].back().first;
        v[nod].pop_back();
        if(!viz[p])
        {
            viz[p]=1;
            euler(next);
        }
    }
    a[++k]=nod;
}

int main()
{
    int x,y;
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back({y,i});
        v[y].push_back({x,i});
    }
    for(int i=1;i<=n;i++)
    {
        if(v[i].size()%2 != 0)
        {
            fout<<-1;
            return 0;
        }
    }
    euler(1);
    for(int i=1;i<k;i++)
        fout<<a[i]<<" ";
}