#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
vector <pair <int,int> > v[100005];
vector <int> sol;
//int g[100005];
bool viz[100005];
int n,m,x,y;
void Ciclu_Eulerian(int x)
{
    while(v[x].size())
    {
        int vec=v[x].back().first;
        int p=v[x].back().second;
        v[x].pop_back();
        if(!viz[p])
        {
            viz[p]=1;
            Ciclu_Eulerian(vec);
        }
    }
    sol.push_back(x);
}
void Read()
{
    fin>>n>>m;
    for(int i=1;i<=m;++i)
    {
        fin>>x>>y;
        v[x].push_back({y,i});
        v[y].push_back({x,i});
    }
    for(int i=1;i<=n;++i)
    {
        if(v[i].size()==0 || v[i].size()%2!=0){fout<<-1;return;}
    }
    Ciclu_Eulerian(1);
    for(int i=0;i<(sol.size()-1);++i)
        fout<<sol[i]<<" ";
}
int main()
{
    Read();
    return 0;
}