#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <utility>
#include <cmath>
#include <string>
#include <cstring>
#define ll long long

using namespace std;

void euler(int node, vector<bool> &vis, vector<vector<pair<int, int>>> &g, vector<int> &ans) {
    if(g[node].size()) {
        auto to = g[node].back();
        g[node].pop_back();
        if(vis[to.second])
            euler(node, vis, g, ans);
        else {
            vis[to.second] = 1;
            euler(to.first, vis, g, ans);
            euler(node, vis, g, ans);
        }
    } else {
        ans.push_back(node);
    }
}

int main() {
    ifstream in("ciclueuler.in");
    ofstream out("ciclueuler.out");

    int n, m;
    in >> n >> m;
    vector<vector<pair<int, int>>> g(n + 1);
    for(int i = 1; i <= m; i ++) {
        int x, y;
        in >> x >> y;
        g[x].push_back({y, i});
        g[y].push_back({x, i});
    }

    for(int i = 1; i <= n; i ++) {
        if(g[i].size() % 2) {
            out << -1;
            return 0;
        }
    }
    vector<bool> vis(m + 1, 0);
    vector<int> ans;
    euler(1, vis, g, ans);
    for(auto it : ans)
        out << it << " ";

    return 0;
}