#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
#include <stack>
#include <queue>
#define inf 1<<30
#define x first
#define y second
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
stack <int > st;
vector <pair<int,int> > v[100050];
int muchii[500050],g[100005],f[100005];
int i,a,b,j,n,m,maxi,l,k,lungime,ok;
void conex(int nod)
{
    int i;
    f[nod] = 1;
    for(i = 0; i < v[nod].size(); i++)
        if(!f[v[nod][i].x])
            conex(v[nod][i].x);
}
int main()
{
    fin >> n >> m;
    for(i = 1; i <= m; i++)
    {
        fin >> a >> b;
        v[a].push_back(make_pair(b,i));
        v[b].push_back(make_pair(a,i));
        g[a]++;
        g[b]++;
    }
    conex(1);
    for(i = 1; i <= n; i++)
        if(g[i]%2 || !f[i])
        {
            fout<<-1;
            return 0;
        }
    st.push(1);
    while(st.size())
    {
        int now = st.top();
        ok = 1;
        while(v[now].size())
        {
            if(!muchii[v[now].back().y])
            {
                muchii[v[now].back().y] = 1;
                st.push(v[now].back().x);
                v[now].pop_back();
                ok = 0;
                break;
            }
            v[now].pop_back();
        }
        if(ok)
        {
            if(st.size() > 1)
                fout<<st.top()<<" ";
            st.pop();
        }
    }

    return 0;
}