#include <fstream>
#include <vector>
#include <cstdio>
#include <stack>
#include <algorithm>
#define VAL 100005
#define MC 500005

using namespace std;

int N, M, i, j, mch;
int A[MC], B[MC], nod, nr;
stack <int> S;
vector <int> G[VAL];
vector <int> :: iterator it;
bool viz[MC], ciclu=true;

char buff[VAL];
int poz=0;

int Read_INT()
{
    int nr=0;
    while (buff[poz]<'0' || buff[poz]>'9')
      if (++poz==VAL)
        fread(buff, 1, VAL, stdin), poz=0;
    while ('0'<=buff[poz] && buff[poz]<='9')
    {
        nr=nr*10+buff[poz]-'0';
        if (++poz==VAL)
          fread(buff, 1, VAL, stdin), poz=0;
    }
    return nr;
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    N=Read_INT();
    M=Read_INT();
    for (i=1; i<=M; i++)
    {
        A[i]=Read_INT();
        B[i]=Read_INT();
        G[A[i]].push_back(i);
        G[B[i]].push_back(i);
    }
    for (i=1; i<=N; i++)
    {
        if (G[i].size() % 2==1)
        {
            ciclu=false;
            break;
        }
    }
    if (ciclu==false)
      printf("-1\n");
    else
    {
        nod=1;
        while (1)
        {
            if (G[nod].empty()==true && S.empty()==true)
              break;
            if (G[nod].empty()==true)
            {
                printf("%d ", nod);
                nod=S.top();
                S.pop();
            }
            else
            {
                S.push(nod);
                mch=G[nod].back();
                G[nod].pop_back();
                if (viz[mch]==false)
                {
                    viz[mch]=true;
                    if (nod==A[i])
                      nod=B[i];
                    else
                      nod=A[i];
                }
            }
        }
    }
    return 0;
}