#include <stdio.h>
#include <stack>
#include <queue>
#define nMax 100100
using namespace std;

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

void citire()
{
    scanf("%d%d",&n,&m);
    for(int i=0;i<m;i++)
    {
        int x;
        int y;
        scanf("%d%d",&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;
            break;
        }
    }
}


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

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

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

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


    return 0;
}