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

ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

using PI = pair<int, int>;

using VI = vector<int>;
using VB = vector<bool>;
using VP = vector<PI>;
using Iter= VP::iterator;
using VVP = vector<VP>;

int n, m;
VVP G;
VB v;
VI c;

struct Egde {
    int x, y;
};

void CitesteDate();
bool Eulerian();
void Ciclu(int x);
void AfisCiclu();

int main()
{
    CitesteDate();
    if (!Eulerian())
        cout << "-1";
    else
        {
            Ciclu(1);
            AfisCiclu();
        }
}

void Ciclu(int x)
{
    vector<Iter> p(n + 1);
    stack<int> stk;

    for (int i = 1; i <= n; ++i)
        p[i] = G[i].begin();

    stk.push(x);
    int y, e;

    while (!stk.empty())
    {
        x = stk.top();
        if (p[x] == G[x].end())
        {
            c.push_back(x);
            stk.pop();
        }
        else
        {
            tie(e, y) = *p[x]++;
            if (v[e]) continue;

            v[e] = true;
            stk.push(y);
        }
    }
}

void AfisCiclu()
{
    for (int x : c)
        cout << x << ' ';
}

bool Eulerian()
{
    for (int x = 1; x <= n; ++x)
        if (G[x].size() % 2 == 1)
            return false;
    return true;
}

void CitesteDate()
{
    cin >> n >> m;
    G = VVP(n + 1);
    v = VB(n + 1);

    int x, y;
    for (int e = 1; e <= m; ++e)
    {
        cin >> x >> y;
        G[x].emplace_back(e, y);
        G[y].emplace_back(e, x);
    }
}