#include <bits/stdc++.h>
#define LMAX 100001

using namespace std;
FILE *fin=fopen("ciclueuler.in","r");
FILE *fout=fopen("ciclueuler.out","w");

int n, m;

vector<int>G[LMAX];

int sol[LMAX];
int nrsol;

void euler(int start);

int x, y;

int cb(int unde, int x);
bool ok=1;

int main()
{
    fscanf(fin,"%d %d",&n,&m);
    for (int i=1;i<=m;i++)
    {
        fscanf(fin,"%d %d",&x,&y);
        //if (x==y) continue;
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for (int i=1;i<=n;i++)
        {
         sort(G[i].begin(),G[i].begin()+G[i].size());
         if (G[i].size()%2)
            ok=0;
        }
    if (!ok)
        fprintf(fout,"-1\n");
        else
        {
         euler(1);
         for (int i=1;i<nrsol;i++)
             fprintf(fout,"%d ",sol[i]);
        }
    fclose(fin);
    fclose(fout);
    return 0;
}

int cb(int unde, int x)
{
    int st=0, dr=G[unde].size()-1;
    int m;
    while (st<=dr)
    {
        m=(st+dr)/2;
        if (G[unde][m]==x)
            return m;
            else if (G[unde][m]>x)
                 dr=m-1;
                else st=m+1;
    }
}

void euler(int start)
{
    int poz, merg;
    if (!start) return ;
    for (int i=0;i<G[start].size();i++)
        if (G[start][i])
        {
         merg=G[start][i];
         G[start].erase(G[start].begin()+i);
         poz=cb(merg,start);
         G[merg].erase(G[merg].begin()+poz);
         euler(merg);
        }
    sol[++nrsol]=start;
}