#include <fstream>
#include <algorithm>
#include <climits>
#include <vector>
#include <queue>
#include <stack>
#include <unordered_map>
#define NMAX 100003
using namespace std;


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

int n, m,k=0;
int grad[NMAX];
bool viz[500003];
int sol[500003];
vector<pair<int, int>>graf[NMAX];

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        grad[x]++;
        grad[y]++;
        graf[x].push_back({ i,y });
        graf[y].push_back({ i,x });
    }

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

    }

    stack<int>stiv;
    stiv.push(1);
    
    while (!stiv.empty())
    {
        int nod = stiv.top();
        if (grad[nod]== 0) {
            sol[k++]=nod;
            stiv.pop();
        }
        else {
            for (int i = 0; i < graf[nod].size(); i++)
            {
                int muchie = graf[nod][i].first;
                if (!viz[muchie])
                {
                    int nd = graf[nod][i].second;
                    grad[nd]--;
                    grad[nod]--;
                    viz[muchie] = true;
                    stiv.push(nd);
                    break;
                }
            }
        }
    }
    if (k != m + 1)
    {
        fout << "-1";
        return 0;
    }
    for (int i = 0; i < k-1; i++)
    {
        fout << sol[i] << " ";
    }
    return 0;
}