#include <fstream>
#include <stack>
#include <queue>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <set>
#include <cstring>
#include <map>
#include <string>
#include <bitset>
#include <unordered_map>
#include <unordered_set>
#define oo 2000000
#define MOD 1000000007
using namespace std;
vector <pair<int, int> > L[100005]; /// first -> nodul, second -> indicele muchiei
bitset <500001> used;
vector <int> cycle;
int n, m;

void Read()
{
    ifstream fin("test.in");
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        L[x].push_back({ y, i });
        L[y].push_back({ x, i });
    }
}

void EulCycle(int start)
{
    stack <int> st;
    st.push(start);
    while (!st.empty())
    {
        int curr = st.top();
        if (!L[curr].empty())
        {
            pair <int, int> muchie = L[curr].back();
            L[curr].pop_back();
            if (!used[muchie.second]) {
                used[muchie.second] = 1;
                st.push(muchie.first);
            }
        }
        else {
            cycle.push_back(curr);
            st.pop();
        }
    }
}

void Solve()
{
    ofstream fout("test.out");
    for (int i = 1; i <= n; i++)
        if (L[i].size() % 2 == 1)
        {
            fout << "-1\n";
            return;
        }
    EulCycle(1);
    for (int i = 0; i < cycle.size() - 1; i++)
        fout << cycle[i] << " ";
}

int main()
{
    Read();
    Solve();
    return 0;
}