#include <bits/stdc++.h>

#pragma optimize GCC ("Ofast")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

///#include <tryhardmode>
///#include <GODMODE::ON>

using namespace std;

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

const int NMAX=5e5+5;

#define cin fin
#define cout fout

vector<pair<int,int>>v[NMAX];
bool viz[NMAX];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    stack<int>stiva;
    vector<int>total;
    int n,m,i,j,x,y;
    cin>>n>>m;
    for(i=1;i<=m;i++)
    {
        cin>>x>>y;
        v[x].push_back(make_pair(y,i));
        v[y].push_back(make_pair(x,i));
    }
    for(i=1;i<=n;i++)
    {
        if(v[i].size()%2==1)
        {
            cout<<-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.second])
            {
                viz[aux.second]=true;
                stiva.push(aux.first);
                p=aux.first;
            }
        }
        stiva.pop();
        total.push_back(p);
    }
    total.pop_back();
    for(auto i:total)
        cout<<i<<" ";
    return 0;
}