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

using namespace std;

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

const int MAXN = 100004, MAXM = 500004;

struct muchie
{
    int x, y;
    bool viz;
    muchie(){viz = 0;};
    muchie(int xx, int yy)
    {
        x = xx, y = yy, viz = 0;
    }
}muchii[MAXM];

int n, m;
vector<int> nod[MAXN], sol;
stack<int> s;

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        muchii[i] = muchie(x, y);
        nod[x].push_back(i);
        nod[y].push_back(i);
    }

    for(int i = 1; i <= n; i++)
        if(nod[i].size()%2 == 1)
        {
            fout << -1;
            return 0;
        }

    s.push(1);
    while(!s.empty())
    {
        int crt = s.top();
        if(nod[crt].size())
        {
            int mh = nod[crt].back();
            crt[nod].pop_back();
            if(!muchii[mh].viz)
            {
                muchii[mh].viz = 1;
                s.push(crt == muchii[mh].x ? muchii[mh].y : muchii[mh].x);
            }
        }
        else
        {
            sol.push_back(crt);
            s.pop();
        }
    }
    for(int i = 0; i < sol.size()-1; i++)
        fout << sol[i] << " ";
    return 0;
}