#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <cstring>
#include <deque>
#include <algorithm>
#include <set>
#define Nmax 100005
#define INF 0x3f3f3f3f
#define ll long long
#define MOD 666013
#define fs first
#define sc second

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n, m;
vector <pair <int, int> > v[Nmax];
vector <int> sol;

bool used[5*Nmax];

void euler(int x)
{
    while (!v[x].empty())
    {
        int y  =v[x].back().first;
        int num=v[x].back().second;
        v[x].pop_back();
        if (used[num] == 1) continue;
        used[num]=1;
        euler(y);
    }
    sol.push_back(x);
}

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

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


    euler(1);
    sol.pop_back();
    for (auto i:sol) g << i << " ";


    return 0;
}