#include <bits/stdc++.h>
#define NMAX 500005
using namespace std;

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


int n, m, len;
int st[NMAX], dr[NMAX];
bool viz[NMAX];
vector <int> L[NMAX];
int rasp[NMAX], poz[NMAX];

bool Euler()
{
    for(int i = 1; i <= n; i++)
        if(L[i].size() % 2)
            return false;
    return true;
}

void dfs(int nod)
{
    int k;
    while(poz[nod] < L[nod].size())
    {
        k = L[nod][poz[nod]++];
        if(!viz[k])
        {
            viz[k] = true;
            dfs(st[k] + dr[k] - nod);
        }
    }
    rasp[++len] = nod;
}

int main()
{
    int x, y;
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        fin >> x >> y;
        st[i] = x;
        dr[i] = y;
        L[x].push_back(i);
        L[y].push_back(i);
    }
    if(!Euler())
    {
        fout <<"-1\n";
        return 0;
    }
    dfs(1);
    for(int i = 1; i <= len; i++)
        fout << rasp[i] << " ";
    return 0;
}