#include <bits/stdc++.h>

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

const int mmax = 500005;
const int nmax = 100005;
struct muchii
{
    int st, dr, ind;
};

vector<muchii> A[mmax];
vector<int> Q;
int n, m, fr[nmax];

static inline void euler(int x)
{
    while(A[x].size())
    {
        muchii k = A[x].back();
        A[x].pop_back();
        if(!fr[k.ind])
        {
            fr[k.ind] = 1;
            euler(k.dr);
        }
    }

    Q.push_back(x);
}

int main()
{
    f.tie();
    f >> n >> m;
    for(int i = 1; i <= m; i ++)
    {
        int x, y;
        f >> x >> y;
        A[x].push_back({x, y, i});
        A[y].push_back({y, x, i});
    }

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

    euler(1);
    for(int i = 0; i < Q.size() - 1; i ++)
        g << Q[i] << " ";

    return 0;
}