#include <iostream>
#include <cstdio>
#include <vector>
#include <bitset>
#include <deque>

using namespace std;
int grad[100005];
vector <int> g[100005];
deque <int> q;
vector <pair<int,int> > muc;
bitset <500004> viz;
int n,m,a,b;
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d", &n,&m);
    for(int i=0;i<m;++i)
    {
        scanf("\n%d %d", &a,&b);
        muc.push_back({a,b});
        g[a].push_back(i), g[b].push_back(i);
        ++grad[a], ++grad[b];
    }
    bool ok=1;
    for(int i=1;i<=n;++i)
        if(grad[i]%2)
            ok=0;
    if(ok)
    {
        q.push_back(1);
        while(!q.empty())
        {
            a=q.front();
            if(g[a].empty())
            {
                q.pop_front();
                if(q.size())
                    cout<<a<<" ";
            }
            else
            {
                b=g[a].back();
                g[a].pop_back();
                if(!viz[b])
                {
                    viz[b]=1;
                    if(muc[b].first==a)
                        q.push_front(muc[b].second);
                    else
                        q.push_front(muc[b].first);
                }
            }
        }
    }
    else
        cout<<"-1";
    return 0;
}