#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <fstream>
#include <tuple>
#include <stack>

using namespace std;

using VI = vector<int>;
using VPI = vector<pair<int, int>>;
using VVPI = vector<VPI>;
using ITVPI = vector<VPI::iterator>;
using VVI = vector<VI>;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m;
VVPI G;
vector<bool> viz;
VI eulerianCycle;

void Euler(int x)
{
    ITVPI p(n + 1);


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

    stack<int> stk;
    stk.emplace(x);
    pair<int, int> y;
    while (!stk.empty())
    {
        x = stk.top();

        if (p[x] == G[x].end())
        {
            eulerianCycle.emplace_back(x);
            stk.pop();
        }
        else
        {
            y = *p[x]++;
            if (viz[y.first])
                continue;

            viz[y.first] = true;
            stk.emplace(y.second);
        }
    }

}

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

    bool possible = true;
    viz = vector<bool>(m + 1);
    for (int i = 1; i <= n; ++i)
        if (G[i].size() & 1)
            possible = false;

    if (!possible)
        fout << -1;
    else
    {
        Euler(1);
        for (int i = 0; i + 1 < eulerianCycle.size(); ++i)
            fout << eulerianCycle[i] << ' ';
    }
}