#include <fstream>
#include <vector>
#define nmax 100002
using namespace std;

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

int n, m;

vector < pair < int, int > > G[nmax];

bool viz[5 * nmax];

vector < int > ans;

void dfs(int k)
{
    while(!G[k].empty())
    {
        int nod = G[k].back().first, muc = G[k].back().second;

        G[k].pop_back();

        if(viz[muc]) continue;

        viz[muc] = 1;
        dfs(nod);
    }
    ans.push_back(k);
}

int main()
{
    fin >> n >> m;

    for(int i = 1; i <= m; ++i)
    {
        int x, y; fin >> x >> y;
        G[x].push_back({y, i});
        G[y].push_back({x, i});
    }

    for(int i = 1; i <= n; ++i)
    {
        if(G[i].size() % 2)
        {
            fout << -1;
            return 0;
        }
    }

    dfs(1);

    ans.pop_back();

    for(auto it : ans)
    {
        fout << it << " ";
    }

    return 0;
}