#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
#define mmax 500005
#define nmax 500005
int a[mmax], b[mmax],sol[500001],nr;
vector <int> G[nmax];
bool viz[nmax];
void euler(int x) {
    int curent, urm;
    while (G[x].size() != 0) {
        curent = G[x].back();
        G[x].pop_back();
        if (viz[curent] == 0) {
            viz[curent] = 1;
            if (a[curent] == x)
                urm = b[curent];
            else
                urm = a[curent];
            euler(urm);
        }
    }
    sol[++nr] = x;
}

int main()
{
    int st, n, m;
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        fin >> a[i] >> b[i];
        G[a[i]].push_back(i);
        G[b[i]].push_back(i);
    }
    st = 0;
    for (int i = 1; i <= n; i++)
        if ((G[i].size() % 2) == 1)
            st = 1;
    if (st == 1)
        fout << -1;
    else {
        euler(1);
        
        for (int r = 1; r < nr; r++)
            fout << sol[r] << " ";
    }
    return 0;
}