#include <fstream>
#include <stack>
#include <bitset>
#include <vector>
using namespace std;

ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

int n,m;
bitset<500002>used;
vector<int>sol;
vector<vector<pair<int,int>>>g;

void citire()
{
    cin>>n>>m;
    g.resize(n+1);
    int x,y;
    for(int i=0;i<m;i++)
    {
        cin>>x>>y;
        g[x].push_back({y,i});
        g[y].push_back({x,i});
    }
}
void ciclu()
{
    stack<int>s;
    s.push(1);
    while(!s.empty())
    {
        int nod=s.top();
        if(g[nod].size()>0)
        {
            pair<int,int>muchie=g[nod].back();
            g[nod].pop_back();
            if(!used[muchie.second])
            {
                used[muchie.second]=1;
                s.push(muchie.first);
            }
        }
        else
        {
            sol.push_back(nod);
            s.pop();
        }
    }
    sol.pop_back();//scap de primul care se repeta la final
}
int main()
{
    citire();
    for(int i=1;i<=n;i++)
        if(g[i].size()%2)
    {
        cout<<-1;
        return 0;
    }
    ciclu();
    for(int x:sol)
        cout<<x<<' ';
    return 0;
}