#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define nmax 100005

using namespace std;

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

int n, m, grad[nmax];
vector <int> G[nmax], sol;
stack <int> st;

void read() {
    int x, y;
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        fin >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
        grad[x]++;
        grad[y]++;
    }
}

bool check() {
    for (int i = 1; i <= n; i++)
        if (grad[i] % 2 == 1)
            return 0;
    return 1;
}

void sterge(int nod, int vc) {
    vector <int>::iterator it;
    for (it = G[nod].begin(); it != G[nod].end(); it++)
        if (*it == vc) {
            G[nod].erase(it);
            return;
        }
}

void euler(int nod) {
    st.push(nod);
    while (!st.empty()) {
        nod = st.top();
        if (G[nod].size() != 0) {
            int vc = G[nod][0]; G[nod].erase(G[nod].begin());
            sterge(vc, nod); // il sterg din G[vc], pe nod
            st.push(vc);
        } else {
            sol.push_back(st.top());
            st.pop();
        }
    }
}

void solve() {
    if (check() == 0) {
        fout << -1 << "\n";
        return;
    }
    euler(1);
    for (int i = 0; i < m; ++i)
        fout << sol[i] << " ";
    fout << "\n";
}

int main() {
    
    read();
    solve();
    
    fin.close();
    fout.close();
    
    return 0;
}