#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
#include <stack>

const int MAXN = 100005;
const int MAXM = 500005;

typedef std::vector< std::pair<int, int> >::iterator iter;

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

int n, m;
std::vector< std::pair<int, int> > G[MAXN];
std::bitset<MAXM> viz;
std::stack<int> stk;


void dfs(int nd = 1)
{
    if (viz[nd] == true) {
        return;
    }
    viz[nd] = true;
    for (iter it = G[nd].begin(); it != G[nd].end(); it++) {
        dfs(it->first);
    }
}

bool checkEuler()
{
    viz.reset();
    dfs();
    for (int i = 1; i <= n; i++) {
        if (viz[i] == false || G[i].size() % 2 != 0) {
            return false;
        }
    }
    return true;
}


void euler(int nod = 1)
{
    stk.push(nod);
    bool start = true;
    while (!stk.empty()) {
        int nd = stk.top();
        if (start == true) {
            stk.pop();
            start = false;
        }

        bool ok = true;
        for (iter it = G[nd].begin(); it != G[nd].end(); it++)
        {
            if (viz[it->second] == true) {
                continue;
            }
            viz[it->second] = true;
            stk.push(it->first);
            ok = false;
            break;
        }
        if (!ok) {
            continue;
        }
        g << nd << ' ';
        stk.pop();
    }
    g << std::endl;
}

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


    if (!checkEuler()) {
        g << -1 << std::endl;
        f.close();
        g.close();
        return 0;
    }

    viz.reset();
    euler();

    f.close();
    g.close();
    return 0;
}