#include <vector>
#include <fstream>
#include <bitset>
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <stack>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m;
vector<pair<int,int>> L[100005];
bitset<500005> viz;
int main()
{
    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 });
    }
    for(int i=1; i<=n; i++)
        if (L[i].size() % 2 == 1)
        {
            fout << -1;
            return 0;
        }
    stack<int> st;
    st.push(1);
    vector<int> sol;    
    while (!st.empty())
    {
        int curr = st.top();
        if (L[curr].empty())
        {
            sol.push_back(curr);
            st.pop();
        }
        else
        {
            pair<int, int> next = L[curr].back();
            L[curr].pop_back();
            if (!viz[next.second])
            {
                viz[next.second] = 1;
                st.push(next.first);
            }
        }
    }
    for (int i=0; i<sol.size()-1; i++)
        fout << sol[i] << " ";
    return 0;
}