#include <iostream>
#include <vector>
#include <fstream>
#include <stack>
#include <algorithm>
using namespace std;

vector <vector <int> > a(100002);
int n, m;
vector <bool> viz(100002);
vector <int> sol;
stack <int> eul;
ofstream g("ciclueuler.out");

void read()
{
    ifstream f("ciclueuler.in");
    f >> n >> m;
    for(int i=0, x, y; i<m; ++i)
    {
        f >> x >> y;
        a[x].push_back(y);
        a[y].push_back(x);
    }
    f.close();
}

void DFS(int x)
{
    viz[x]=true;
    for(int i=0; i<a[x].size(); ++i)
    {
        if(!viz[a[x][i]])
            DFS(i);
    }
}

int eulerian()
{
    DFS(1);
    for(int i=1; i<=n; ++i)
        if(!viz[i] || a[i].size()%2 )
        return 0;
    return 1;
}

void solve()
{
    int x, y;
    eul.push(1);
    while(!eul.empty())
    {
        x=eul.top();
        if(a[x].size())
        {
            y=a[x].back();
            a[x].pop_back();
            a[y].erase(find(a[y].begin(),a[y].end(),x));
            eul.push(y);
        }
        else
        {
            x=eul.top();
            eul.pop();
            sol.push_back(x);
        }
    }
    for(int i=0; i<sol.size()-1; ++i)
        g << sol[i] << ' ';
    g << '\n';
    g.close();
}

int main()
{
    read();
    if(!eulerian)
        g << -1 << '\n';
    else
        solve();
    return 0;
}