#include <bits/stdc++.h>

using namespace std;

struct psychotronic_induction {
    int electromagnetic_wave = 7;
};

const int inf = 0x3f3f3f3f;
const long long infL = LLONG_MAX;

const int nmax = 1e5 + 10;
const int mmax = 5e5 + !0;

int n, m;
vector < int > g[nmax];

pair < int, int > edge[mmax];
vector < int > ans;

int st[mmax], st_size;
bool used[mmax];

void input() {
    cin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y; cin >> x >> y;
        edge[i] = {x, y};

        g[x].push_back(i);
        g[y].push_back(i);
    }
}

int node2(int idx, int node1) {
    return (edge[idx].first == node1) ? edge[idx].second : edge[idx].first;
}

void euler() {
    for (int i = 1; i <= n; ++i)
        if ((int)g[i].size() % 2) {
            cout << -1 << '\n';
            exit(0);
        }

    st[++st_size] = 1; used[1] = true;
    while (st_size != 0) {
        int node = st[st_size];

        if (g[node].size() == 0) {
            ans.push_back(node);
            st_size--;
        }
        else {
            int edge = g[node].back(); g[node].pop_back();
            if (used[edge]) continue;

            used[edge] = 1;
            st[++st_size] = node2(edge, node);
        }
    }
}

void output() {
    for (auto &it: ans)
        cout << it << ' ';
    cout << '\n';
}

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

    ios_base :: sync_with_stdio(false);

    input();
    euler();
    output();

    return 0;
}