#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

#define maxN 100001

using namespace std;

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

int n,m;
vector < int > v[maxN];

void readData()
{
    int x,y;
    fin>>n>>m;
    while (m--)
    {
        fin>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
}

void erasePath(int f, int s)
{
    for (int i=0; i<v[f].size(); ++i)
        if (v[f][i]==s)
        {
            v[f].erase(v[f].begin()+i);
            return;
        }
}

void Euler(int root)
{
    stack <int> S;
    S.push(root);
    while (!S.empty())
    {
        int x=S.top();
        if (v[x].size())
        {
            int son=v[x].back();
            v[x].pop_back();
            erasePath(son,x);
            S.push(son);
        }
        else {
            S.pop();
            fout<<x<<' ';
        }
    }
}

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