#include <fstream>
#include <cstring>
#include <vector>
#include <algorithm>
#include <stack>
#include <iomanip>

using namespace std;

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

stack <int> st;
vector <int> ans;
vector <pair <int, int> > v[100010];
int n,m,i,j;
bool use[500010];

int main()
{
    fin >> n >> m;
    for (i=1; i<=m; i++)
    {
        int a,b;
        fin >> a >> b;
        v[a].push_back(make_pair(b,i));
        v[b].push_back(make_pair(a,i));
    }
    for (i=1; i<=n; i++)
        if (v[i].size()%2!=0||v[i].size()==0)
        {
            fout << "-1\n";
            return 0;
        }
    int x=1;
    st.push(x);
    while (!st.empty())
    {
        x=st.top();
        while (v[x].size()>0)
        {
            while (v[x].size()>0&&use[v[x][v[x].size()-1].second])
                v[x].pop_back();
            if (v[x].size()==0)
                break;
            int y=v[x][v[x].size()-1].first;
            use[v[x][v[x].size()-1].second]=1;
            st.push(y);
            x=y;
        }
        ans.push_back(st.top());
        st.pop();
    }
    for (i=0; i<ans.size(); i++)
        fout << ans[i] << ' ';
    fout << '\n';
}