#include <fstream>
#include <algorithm>
#include <vector>
using namespace std;
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");
#define NMAX 100005
#define MMAX 500005
int n,m,from[MMAX],to[MMAX];
vector <int> g[NMAX];
bool usededge[MMAX];
int main()
{
    int x,y;
    cin>>n>>m;
    for(int i=0; i<m; i++)
    {
        cin>>x>>y;
        g[x].push_back(i);
        g[y].push_back(i);
        from[i]=x,to[i]=y;
    }
    for(int i=1; i<=n; i++)
    {
        if(g[i].size() & 1)
        {
            cout<<"-1\n";
            return 0;
        }
    }
    vector <int> stk;
    vector <int> ans;
    stk.push_back(1);
    while(!stk.empty())
    {
        int node=stk.back();
        if(!g[node].empty())
        {
            int aux=g[node].back();
            g[node].pop_back();
            if(!usededge[aux])
            {
                usededge[aux]=true;
                int to= ::from[aux] ^ ::to[aux] ^ node;
                stk.push_back(to);
            }
        }
        else
        {
            stk.pop_back();
            ans.push_back(node);
        }
    }
    for(int i=0; i<ans.size()-1; i++)
    {
        cout<<ans[i]<<" ";
    }
    return 0;
}