#include <bits/stdc++.h>
#define Dmax 100005

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

struct triple{
        int first,second;bool third;
};

vector < triple > M;
vector < int > G[Dmax],sol;
stack < int  > S;
int n,m;
bool ExistaEuler()
{
    for(int i = 1; i <= n; i++)
        if(G[i].size() % 2)
        return false;

    return true;


}

int main()
{
    f>>n>>m;
    for(int i = 1; i <= m; i++)
    {
            int x,y;
            f>>x>>y;
            M.push_back(triple{x,y,false});
            G[x].push_back(M.size() - 1);
            G[y].push_back(M.size() - 1);
    }

    if(!ExistaEuler())
        return -1;

    S.push(1);
    while(!S.empty())
    {
        int nod = S.top();
        if(G[nod].empty())
        {
            sol.push_back(nod);
            S.pop();
        }
        else
        {
            int muchie = G[nod].back();
            G[nod].pop_back();
            if(!M[muchie].third)
            {
                M[muchie].third = true;
                if(M[muchie].second == nod)
                    S.push(M[muchie].first);
                    else
                    S.push(M[muchie].second);
            }


        }

    }
    if(sol.size()!=m+1)
        return -1;
    else
    {
        for(unsigned int i = 0; i < sol.size()-1; i++)
            g<<sol[i]<<" ";
    }


    return 0;
}