#include <fstream>
#include <algorithm>
#include <list>
#include <deque>
#define N 100010
using namespace std;

ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");

int n,m;
list <int> v[N];
list<int>::iterator it;
deque <int> q;

int main()
{
    int x,y,i,ok=1;
    in>>n>>m;
    for(i=1;i<=m;i++)
    {
        in>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for(i=1;i<=n;i++)
        if(v[i].size()%2)
        {
            ok=0;
            break;
        }
    if(!ok)
    {
        out<<"-1\n";
        return 0;
    }

    q.push_front(1);
    while(!q.empty())
    {
        x=q.front();
        if(v[x].size()==0)
        {
            out<<x<<" ";
            q.pop_front();
        }
        else
        {
            y=v[x].front();
            v[x].pop_front();
            q.push_front(y);

            for(it=v[y].begin();it!=v[y].end();it++)
            {
                if(*it==x)
                {
                    v[y].erase(it);
                    break;
                }
            }
        }
    }
    return 0;
}