#include <fstream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <stack>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

const int MAXN = 100005;
const int MAXM = 500005;
int n, m;
vector<pair<int, int>> v[MAXN];
vector<int> sol;
stack<int> s;
bool u[MAXM];

int main() {

    fin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int a, b;
        fin >> a >> b;
        v[a].push_back({b, i});
        v[b].push_back({a, i});
    }

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

    s.push(1);
    while(!s.empty()) {
        int node = s.top();
        if (!v[node].empty()) {
            pair<int, int> k = v[node][v[node].size() - 1];
            v[node].pop_back();
            if (u[k.second] == 0) {
                u[k.second] = 1;
                s.push(k.first);
            }
        }
        else {
            sol.push_back(s.top());
            s.pop();
        }
    }

    for (int i = 0; i < sol.size(); ++i) {
        fout << sol[i] << ' ';
    }

    fout.close();
    return 0;
}