#include <bits/stdc++.h>

using namespace std;

const int len = 500005;
int n, m, x, y;
bool seen[len];
vector<pair<int, int> > g[len];
vector<int> sol;

void dfs(int node) {
    while (!g[node].empty()) {
        pair<int, int> curr = g[node].back();
        g[node].pop_back();
        if (!seen[curr.second]) {
            seen[curr.second] = true;
            dfs(curr.first);
        }
    }
    sol.push_back(node);
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        cin >> x >> y;
        g[x].push_back({y, i});
        g[y].push_back({x, i});
    }

    for (int i = 0; i < n; i++)
        if (g[i].size() & 1)
            return cout << "-1\n", 0;

    dfs(1);

    for (auto& it : sol)
        cout << it << " ";
}