#include <bits/stdc++.h>
#define ll long long
#define nl '\n'
#define FOR(i, a, b) for (int i = a; i <= b; ++i) 
#define F0R(i, a, b) for (int i = a; i >= b; --i)
#define FORd(i, n) for (int i = 0; i < n; ++i)
#define F0Rd(i, n) for (int i = n - 1; i >= 0; --i)
#define trav(a, x) for (auto &a : x)
#define uid(a, b) uniform_int_distribution<int>(a, b)(rng)
using namespace std;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int mxN = 1e5 + 5;

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

int N, M;
vector<pair<int, int>> edges[mxN];
bitset<5 * mxN> used;

void euler(int node) {
    while (edges[node].size()) {
        int next_node = edges[node].back().second;
        int curr_muchie = edges[node].back().first;
        edges[node].pop_back();
        if (!used[curr_muchie]) {
            used[curr_muchie] = true;
            euler(next_node);
        }
    }
    fout << node << " ";
}

void solve() {
    fin >> N >> M;
    for (int i = 0; i < M; ++i) {
        int x, y;
        fin >> x >> y;
        edges[x].push_back({i, y});
        edges[y].push_back({i, x});
    }
    for (int i = 1; i <= N; ++i) {
        if (edges[i].size() % 2) {
            fout << -1;
            return;
        }
    }
    euler(1);
}

int main() {
    fin.tie(0); fout.tie(0);
    ios::sync_with_stdio(0);
    int T = 1;
//    cin >> T;
    while (T--) {
        solve();
    }
    return 0;
}

//read the question correctly (ll vs int)
//what's the meaning of the problem ? Think outside the BOX !!!
//edge cases ?
//make it simple
//write everything (observations, edge cases, ideas, steps, methods, ...)