#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <queue>
using namespace std;
//ifstream fin("ciclueuler.in");
//ofstream fout("ciclueuler.out");
int n,m;
int x,y;
vector<vector<pair<int,int>>>v;
vector<int>sol;
bool ciclue_eurlerian()
{
    for(int i=1;i<=n;i++)
    if(v[i].size()%2==1)
    return 0;

    queue<int>q;
    vector<bool>seen;
    seen.resize(n+1,0);

    q.push(1);
    while(!q.empty())
    {
        int a=q.front();
        q.pop();
        for(auto i:v[a])
        {
            if(seen[i.first]==0)
                {
                    q.push(i.first);
                    seen[i.first]=1;
                }
        }
    }
    for(int i=1;i<=n;i++)
    if(seen[i]==0)
    return 0;


    vector<int>drum;

    stack<int>st;
    st.push(1);
    vector<bool>used;
    used.resize(m+1,0);

    while(!st.empty())
    {
        int a=st.top();

        bool ok=0;
        int id;
        int nod_vecin;

        for(auto i:v[a])
        {
            if(used[i.second]==0)
            {
                ok=1;
                id=i.second;
                nod_vecin=i.first;
                break;
            }
        }
        if(ok)
        {
            st.push(nod_vecin);

            used[id]=1;
        }
        else
        {
            st.pop();
            drum.push_back(a);
        }
    }

    sol=drum;
    return 1;
}
#define fin cin
#define fout cout
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    fin>>n>>m;
    v.resize(n+1);
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back({y,i});
        v[y].push_back({x,i});
    }
    if(ciclue_eurlerian())
    for(int i=0;i<sol.size()-1;i++)
    fout<<sol[i]<<" ";
    else
    fout<<-1;

    return 0;
}