#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>

///PRACTICE

using namespace std;

ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

const int NMAX=1e5+5;

stack<int>stiva;
vector<int>total;
vector<pair<int,int>>v[5*NMAX];

bool viz[5*NMAX];

int main()
{
    int n,m,i,j,x,y;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back(make_pair(i,y));
        v[y].push_back(make_pair(i,x));
    }
    for(i=1;i<=n;i++)
    {
        if(v[i].size()%2==1)
        {
            fout<<-1<<"\n";
            exit(0);
        }
    }
    stiva.push(1);
    while(!stiva.empty())
    {
        int p=stiva.top();
        while(!v[p].empty())
        {
            pair<int,int>aux=v[p].back();
            v[p].pop_back();
            if(!viz[aux.first])
            {
                viz[aux.first]=true;
                stiva.push(aux.second);
                p=aux.second;
            }
        }
        total.push_back(p);
        stiva.pop();
    }
    total.pop_back();
    for(auto i:total)
        fout<<i<<" ";
    return 0;
}