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

const int NMAX = 100005;
const int MMAX = 500005;

struct Edge
{
    int to, id;
};

vector<Edge> v[NMAX];
int n, m, k;
bitset<MMAX + 1> vap;
int last_ind[NMAX + 1];
int ans[MMAX + 5];
int rang[NMAX + 1];

void read()
{
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int st, dr;
        cin >> st >> dr;
        v[st].push_back({dr, i});
        v[dr].push_back({st, i});
        rang[st]++;
        rang[dr]++;
    }
}

void dfs(int nod)
{
    while(!v[nod].empty())
    {
        Edge curr = v[nod].back();
        v[nod].pop_back();

        int i = curr.to;
        int pos = curr.id;

        if(vap[pos] == 0)
        {
            vap[pos] = 1;
            dfs(i);
        }
    }
    ans[++k] = nod;
}

void solve()
{
    for(int i = 1; i <= n; i++)
        if(rang[i] % 2 == 1)
        {
            cout << -1;
            return;
        }
    dfs(1);
    if(k != m+1)
    {
        cout << -1;
        return;
    }
    for(int i = 1; i <= k; i++)
        cout << ans[i] << ' ';
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    read();
    solve();
    return 0;
}