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


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


const int MAXN = 100005;
const int MAXM = 500005;
// <parsing>
const int MAXB = 8192;
FILE* f = fopen("ciclueuler.in", "r");
char buf[MAXB]; int ptr = MAXB;
int getInt()
{
    while (buf[ptr] < '0' || '9' < buf[ptr]) {
        if (++ptr >= MAXB) {
            fread (buf, MAXB, 1, f);
            ptr = 0;
        }
    }
    int nr = 0;
    while ('0' <= buf[ptr] && buf[ptr] <= '9') {
        nr = nr * 10 + buf[ptr] - '0';
        if (++ptr >= MAXB) {
            fread(buf, MAXB, 1, f);
            ptr = 0;
        }
    }
    return nr;
}
// </parsing>
std::ofstream g("ciclueuler.out");
std::vector< std::pair<int, int> > G[MAXN]; int n, m;
std::bitset<MAXM> viz;
std::vector<int> sol;
std::stack<int> st;


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


void euler(int node)
{
    st.push(node);
    while (!st.empty()) {
        int nd = st.top();

        bool breaked = false;
        for (iter it = G[nd].begin(); it != G[nd].end(); it++) {
            if (!viz[it->second]) {
                viz[it->second] = true;
                st.push(it->first);
                breaked = true; break;
            }
        }
        if (!breaked) {
            sol.push_back(nd);
            st.pop();
        }
    }
}


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


    if (!is_euler()) {
        g << -1 << '\n';
        fclose(f);
        g.close();
        return 0;
    }


    euler(1);

    for (int i = 1; i < sol.size(); i++) {
        g << sol[i] << ' ';
    }
    g << '\n';


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