// Source: https://usaco.guide/general/io

#include <bits/stdc++.h>
using namespace std;
//Un graf admite ciclu eulerian <=> graful este conex si toate nodurile sunt de grad par

const int NMAX = 1e5;
const int MMAX = 5e5;

vector<pair<int, int>> G[NMAX + 1];
int grad[NMAX + 1];
int vis[NMAX + 1];
int visM[NMAX + 1];
vector<int> ciclu;

void cicluEulerian(int node) {
    while(G[node].size() > 0) {
        int vecin = G[node].back().first;
        int id = G[node].back().second;
        G[node].pop_back();
        if(!visM[id]) {
            visM[id] = 1;
            cicluEulerian(vecin);
        }
    }
    ciclu.push_back(node);
}

void dfs(int node) {
    vis[node] = 1;
    for(int i = 0; i < G[node].size(); i++) {
        int vecin = G[node][i].first;
        if(!vis[vecin]) {
            dfs(vecin);
        }
    }
}


int main() {
    ifstream cin("ciclueuler.in");
    ofstream cout("ciclueuler.out");
    int n, m;
    cin >> n >> m;
    for(int i = 1; i <= m; i++) {
        int x, y;
        cin >> x >> y;
        grad[x]++;
        grad[y]++;
        G[x].push_back({y, i});
        G[y].push_back({x, i});
    }
    dfs(1);
    bool ok = 1;
    for(int i = 1; i <= n; i++) {
        if(!vis[i] || grad[i] % 2 == 1) {
            ok = 0;
        }
    }
    if(ok == 0) {
        cout << -1;
    } else {
        cicluEulerian(1);
        for(int i = 0; i < ciclu.size() - 1; i++) {
            cout << ciclu[i] << ' ';
        }

    }
}