#include <bits/stdc++.h>

using namespace std;

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

int n,m,i,x,y,gr[100001],viz[500001];
vector<pair<int,int>> v[100001];

void ciclu(int l)
{
    while (!v[l].empty())
    {
        pair<int,int> t=v[l].back();
        v[l].pop_back();
        if (viz[t.second])
        viz[t.second]=0, ciclu(t.first);
    }
    fout<<l<<" ";
}

int main()
{
    int ok=1;
    fin>>n>>m;
    for (i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back(make_pair(y,i));
        v[y].push_back(make_pair(x,i));
        gr[x]++;
        gr[y]++;
        viz[i]=1;
    }
    for (i=1;i<=m;i++)
        if (gr[x]%2==1)
            ok=0;
    if (ok)
        ciclu(1);
    else fout<<-1;
    return 0;
}