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

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;
int stk[500005], ptr = -1;


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 checkEuler1()
{
    for (int i = 1; i <= n; i++) {
        if ((G[i].size() & 1) != 0) {
            return false;
        }
    }
    return true;
}

bool checkEuler2()
{
    viz.reset();
    dfs();
    for (int i = 1; i <= n; i++) {
        if (viz[i] == false) {
            return false;
        }
    }
    return true;
}

void euler(int nod = 1)
{
    stk[++ptr] = nod;
    bool start = true;
    while (ptr >= 0) {
        int nd = stk[ptr];
        if (start == true) {
            start = false;
            stk[--ptr] = 0;
        }

        if (!G[nd].empty())
        {
            stk[++ptr] = G[nd][0].first;

            G[G[nd][0].first].erase(std::find(G[G[nd][0].first].begin(), G[G[nd][0].first].end(), std::make_pair(nd, G[nd][0].second)));
            G[nd].erase(G[nd].begin());

            continue;
        }
        g << nd << ' ';
        stk[ptr--] = 0;
    }
    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 (!checkEuler1()) {
        g << -1 << std::endl;
        f.close();
        g.close();
        return 0;
    }
    if (!checkEuler2()) {
        g << -1 << std::endl;
        f.close();
        g.close();
        return 0;
    }

    euler();

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