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

using namespace std;
ifstream fi("ciclueuler.in");
ofstream fo("ciclueuler.out");
const int nmax=1e5;
int n, m;
int used[5*nmax+5];
vector <int> sol;
vector <pair <int, int> > G[nmax+5];
stack <int> S;

int main()
{
    fi>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x, y;
        fi>>x>>y;
        G[x].push_back({y, i});
        G[y].push_back({x, i});
    }

    for(int i=1; i<=n; i++)
        if(G[i].size()&1)
        {
            fo<<-1;
            return 0;
        }

    S.push(1);
    while(!S.empty())
    {
        int nod=S.top();
        while(!G[nod].empty())
            if(used[G[nod].back().second])
                G[nod].pop_back();
            else
                break;
        if(!G[nod].empty())
        {
            pair <int, int> vec=G[nod].back();
            G[nod].pop_back();
            used[vec.second]=1;
            S.push(vec.first);
        }
        else
        {
            sol.push_back(nod);
            S.pop();
        }
    }

    sol.pop_back();
    for(auto i:sol)
        fo<<i<<" ";

    fi.close();
    fo.close();
    return 0;
}