#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 1, M = 5e5 + 1;

int n, m, x, y;
vector<pair<int, int>> mc[N];
stack<int> st;
vector<int> ans;
bool vis[M];

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    ios::sync_with_stdio(false);
    cin.tie(0);

    cin >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        cin >> x >> y;
        mc[x].push_back({y, i});
        mc[y].push_back({x, i});
    }
    for (int i = 1; i <= n; ++i)
    {
        if (mc[i].size() % 2)
        {
            cout << -1;
            return 0;
        }
    }

    st.push(1);
    for (int i = 1; i <= m; ++i)
    {
        if (st.empty())
        {
            cout << -1;
            return 0;
        }
        int nod = st.top();
        while (!mc[nod].empty())
        {
            int nxt = mc[nod].back().first, idx = mc[nod].back().second;
            mc[nod].pop_back();
            if (vis[idx])
                continue;
            vis[idx] = 1;
            st.push(nxt);
            nod = nxt;
        }
        st.pop();
        ans.push_back(nod);
    }

    if (ans.size() != m)
    {
        cout << -1;
        return 0;
    }
    for (auto i : ans)
        cout << i << ' ';

    return 0;
}