#include <bits/stdc++.h>
#define Nmax 500005

using namespace std;

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

int N, st[Nmax], dr[Nmax], poz[Nmax], ans[Nmax], top;
vector <int> L[Nmax];
bool used[Nmax];

inline void Read()
{
    int i, M;
    fin >> N >> M;
    for(i = 1; i <= M; i++)
    {
        fin >> st[i] >> dr[i];
        L[st[i]].push_back(i);
        L[dr[i]].push_back(i);
    }
}

inline bool Cicle()
{
    for(int i = 1; i <= N; i++)
        if(L[i].size() & 1) return false;
    return true;
}

inline void DFS(int nod)
{
    while(L[nod].size() > poz[nod])
    {
        int k = L[nod][poz[nod]++];
        if(!used[k])
        {
            used[k] = 1;
            DFS(st[k] + dr[k] - nod);
        }
    }
    ans[++top] = nod;
}

inline void Solve()
{
    if(!Cicle()) fout << "-1\n";
    else
    {
        DFS(1);
        for(int i = 1; i <= top; i++)
            fout << ans[i] << " ";
    }
    fout.close();
}

int main()
{
    Read();
    Solve();
    return 0;
}