#include <iostream>
#include <fstream>
#include <stack>
#include <vector>

using namespace std;
vector < vector< pair<int, int> > > v;
vector <int> sol;
int main() {
    int n, m;
    ifstream cin("ciclueuler.in");
    ofstream cout ("ciclueuler.out");
    cin >> n >> m;
    v.resize(n + 1);
    bool seen[m + 1];
    
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        seen[i + 1] = false;
        v[a].push_back(make_pair(b, i + 1));
        v[b].push_back(make_pair(a, i + 1));
    }

    for (int i = 1; i <= n; i++) {
        if (v[i].size() % 2 != 0) {
            cout << "-1";
            return 0;
        }
    }

    stack <int> s;

    s.push(1);

    while (!s.empty()) {
        int k = s.top();

        if (v[k].size() == 0) {
            sol.push_back(k);
            s.pop();
        } else { 
            int edge = v[k].back().second;
            int node = v[k].back().first;

            v[k].pop_back();

            if (!seen[edge]) {
                seen[edge] = true;
                s.push(node);
            }
        }
    }

    for (int i = 0; i < sol.size() - 1; i++) {
        cout << sol[i] << " ";
    }
    return 0;
}