#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#define DM 100005
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m, a, b, st[DM*5], top;
vector <int> g[DM];

void parcurgere_euler(int nod)
{
    while(g[nod].size())
    {
        int act = g[nod].back();
        g[nod].pop_back();
        g[act].erase(find(g[act].begin(),g[act].end(),nod));
        parcurgere_euler(act);
    }
    fout << nod << ' ';
}
void parcurgere_euler_iterativ()
{
    st[++top] = 1;
    while(top > 0)
    {
        int nod = st[top];
        top--;

        if(g[nod].size())
        {
            int act = g[nod].back();
            g[nod].pop_back();
            g[act].erase(find(g[act].begin(),g[act].end(),nod));
            st[++top] = act;
        }
        fout<<nod<<' ';
    }
}
int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        fin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    for(int i = 1; i <= n; i++)
        if(g[i].size() % 2 != 0)
        {
            fout<<"-1";
            return 0;
        }
    parcurgere_euler_iterativ();
    return 0;
}