#include <fstream>
#include <vector>
#include <bitset>
using namespace std;

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

struct Edge {
    int a, b;
};
using VI = vector<int>;
using VVI = vector<vector<int>>;
using VE = vector<Edge>;

const int MaxN = 100001;
const int MaxM = 500001;

bitset<MaxN> v;

VVI G;
VE E;
VI ce; // ciclu eulerian
int n, m;

void Citire();
void Afisare();
bool EsteEulerian();
inline void DF(int x);

int main()
{
    Citire();
    if(!EsteEulerian())
        fout << "-1";
    else
    {
        DF(1);
        Afisare();
    }

    return 0;

}
void Citire()
{
    int x, y;
    fin >> n >> m;
    G = VVI(n + 1);
    E = VE(m + 1);

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

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

void Afisare()
{
    for (size_t i = 0; i < ce.size() - 1; ++i)
    {
        fout << ce[i] << ' ';
    }
}

inline void DF(int x)
{
    for (const int &e : G[x])
    {
        if (v[e]) continue;
        v[e] = 1;
        if (E[e].a == x)
            DF(E[e].b);
        else DF(E[e].a);
    }

    ce.emplace_back(x);
}