#include <iostream>
#include <cstdio>
#include <stack>
#include <list>
#include <queue>
#include <vector>
#define Nmax 100010
using namespace std;

list <int> Graf[Nmax];
vector <int>Sol;
stack <int> S;
queue <int> Coada;
int N,M;
int Grad[Nmax],Viz[Nmax];

void Citire()
{
    int x,y;
    scanf("%d %d",&N,&M);
    for(int i=0;i<M;++i)
    {
        scanf("%d %d",&x,&y);
        Graf[x].push_back(y);
        Graf[y].push_back(x);
        Grad[x]++;Grad[y]++;
    }
}

void BFS()
{
    Coada.push(1);
    Viz[1]=1;
    while(!Coada.empty())
    {
        int x=Coada.front();
        Coada.pop();
        list<int>::iterator it;
        for(it=Graf[x].begin();it!=Graf[x].end();++it)
        {
            if(!Viz[*it])
            {
                Viz[*it]=1;
                Coada.push(*it);
            }
        }
    }
}

int Este_eulerian()
{
    BFS();
    for(int i=1;i<=N;++i)
        if(Viz[i]==0)
            return 0;
    for(int i=1;i<=N;++i)
        if(Grad[i]%2!=0)
            return 0;
    return 1;
}

void Sterge(int v,int w)
{
    Graf[v].pop_front();
    list<int>::iterator it;
    for(it=Graf[w].begin();it!=Graf[w].end();++it)
        if(*it==v)
        {
            Graf[w].erase(it);
            break;
        }
}

void Euler(int v)
{
    while(!Graf[v].empty())
    {
        int w=Graf[v].front();
        S.push(v);
        Sterge(v,w);
        v=w;
    }
}

void Rezolvare()
{
    int v;
    S.push(1);
    while(!S.empty())
    {
        v=S.top();
        S.pop();
        Euler(v);
        Sol.push_back(v);
    }
}

void Afisare()
{
    for(int i=0;i<Sol.size()-1;++i)
        printf("%d ",Sol[i]);
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    Citire();
    if(!Este_eulerian())
        printf("-1");
    else
    {
        Rezolvare();
        Afisare();
    }
    return 0;
}