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

using namespace std;

ifstream f("in.in");
struct three{
        int first,second; bool third;
};
vector < three > M;
vector < int > sol,G[Dmax];
stack < int > S;
int n,m;
bool EsteEuler()
{
    for(int i = 1; i <= n; i++)
        if(G[i].size() & 1)
        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(three{x,y,false});
        G[x].push_back(i);
        G[y].push_back(i);
    }

    if(!EsteEuler)
    {
        cout<<"-1\n";
        return 0;
    }

    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();
            muchie--;
            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)
    {
        for(unsigned int i = 0; i < sol.size() - 1; i++)
            cout<<sol[i]<<" ";
    }
    else
    {
        cout<<"-1\n";
        return 0;
    }


    return 0;
}