#include <fstream>
#include <iostream>
#include <vector>
#include <list>
#define bsize (1<<16)+1
using namespace std;

vector <int> v[100003];
vector <int> :: iterator it;
list <int> q;
int i,y,n,nr,m,of,pos;
char ch[bsize+1];
int read (int &x)
{
    x=0;
    while (!isdigit(ch[pos]))
    {

        if (pos==bsize)
        {
            fread(ch,bsize,1,stdin);
            pos=0;
        }
        else
        {
            pos++;
        }
    }
    if (pos==bsize)
    {
        fread(ch,bsize,1,stdin);
    }
    while (isdigit(ch[pos]))
    {
        x=x*10+(ch[pos]-'0');
        if (pos==bsize)
        {
            fread(ch,bsize,1,stdin);
            pos=0;
        }
        else
        {
            pos++;
        }
    }
    return x;
}
int x;
int main()
{
    ios_base :: sync_with_stdio (false);
    freopen ("ciclueuler.in","r",stdin);
    freopen ("ciclueuler.out","w",stdout);
    fread (ch,bsize,1,stdin);
    read(n);
    read(m);
    for (i=1;i<=m;i++)
    {
        read(x);
        read(y);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for (i=1;i<=n;i++)
    {
        if (v[i].size()%2!=0)
        {
            cout<<"-1";
            return 0;
        }
    }
    q.push_back(1);
    while (!q.empty())
    {
        of=q.front();
        x=of;
        if (v[of].size()==0)
        {
            if (nr<m)
            {
                cout<<of<<" ";
                nr++;
            }
            q.pop_front();
        }
        else
        {
            y=v[x].back();
            q.push_front(y);
            v[x].pop_back();
             for (it=v[y].begin();it!=v[y].end();it++)
    {
        if (*it==x)
        {
            v[y].erase(it);
            break;
        }
    }
        }
    }

    return 0;
}