#include <bits/stdc++.h>

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

vector < pair <int,int > > v[100100];
int t,sol[500100],fv[500100];

void ciclu(int nod)
{
    for(int i=0;i<v[nod].size();i++)
    {
        int vecin=v[nod][i].first;
        int indice_muchie=v[nod][i].second;

        if(fv[indice_muchie]==0)
        {
            fv[indice_muchie]=1;
            ciclu(vecin);
        }
    }

    t++;sol[t]=nod;
}

int n,m,i,x,y;
int main()
{
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back({y,i});
        v[y].push_back({x,i});
    }

    /// intai verificam conditia necesara si suficienta
    for(i=1;i<=n;i++)
    {
        if(v[i].size()%2==1)
        {
            g<<-1;
            return 0;
        }
    }

    ciclu(1);
    for(i=t;i>=2;i--)g<<sol[i]<<" ";
    return 0;
}