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