#include <stdio.h>
#include <stack>
#include <queue>
#include <algorithm>
#define nMax 100100
#define max(a,b) ((a<b)?a:b)
using namespace std;

int n;
int m;
int grad[nMax];
int viz[nMax];
int coada[nMax];
int nCoada;

struct nod{
    int x;
    nod *urm;
}*a[nMax];
stack <int> s;
queue <int> afis;



void citire()
{
    scanf("%d %d\n",&n,&m);
    for(int i=0;i<m;i++)
    {
        int x;
        int y;
        scanf("%d %d\n",&x,&y);
        grad[x]++;
        grad[y]++;
        nod *g;
        g = new nod;
        g -> x = x;
        g -> urm = a[y];
        a[y] = g;
        nod *h;
        h = new nod;
        h -> x = y;
        h -> urm = a[x];
        a[x]=h;
    }
}

void sterge(int x, int y)
{
    if(a[x]->x == y)
    {
        a[x]=a[x]->urm;
        return;
    }
    for(nod *i=a[x]; i->urm; i=i->urm)
    {
        if(i->urm->x==y)
        {
            i->urm=i->urm->urm;
            return;
        }
    }
}


void euler(int v)
{
    while(a[v])
    {
        int undeMerge=a[v]->x;
        s.push(undeMerge);
        a[v]=a[v]->urm;
        sterge(undeMerge,v);
        v=undeMerge;
    }
}

void intelegemSolutiaLorSiIncercamSaOScriemSiNoi(int v) //functie denumita de PI
{
    do{
        euler(v);
        v=s.top();
        s.pop();
        afis.push(v);
    }while(!s.empty());
}

void bfs(int k)
{
    coada[nCoada++]=k;
    viz[k]=1;
    for(int i=0;i<nCoada;i++)
    {
        for( nod *j=a[coada[i]];j;j=j->urm)
        {
            if(!viz[j->x])
            {
                viz[j->x]=viz[coada[i]]+1;
                coada[nCoada++]=j->x;
            }
        }
    }
    for(int i=1;i<=n;i++)
        if(viz[i]==0)
        {
            printf("-1\n");
            exit(0);
        }
}



void rez()
{
    for(int i=0;i<=n;i++)
    {
        if(grad[i]!=0)
        {
            bfs(i);
            intelegemSolutiaLorSiIncercamSaOScriemSiNoi(i);
            return;
        }
    }
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    citire();
    for(int i=0;i<=n;i++)
    {
        if(grad[i]==0)
            viz[i]=1;
        if(grad[i]%2==1)
        {
            printf("-1\n");
            return 0;
        }
    }
    rez();
    while(!afis.empty())
    {
        printf("%d ",afis.front());
        afis.pop();
    }
    printf("\n");


    return 0;
}