#include <bits/stdc++.h>
#define pb push_back

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
const int MAXN = 100010, MAXM = 500010;

struct Edge {
    int from, to;
    bool vis;
}edges[MAXM];
vector<int> graph[MAXN];
stack<int> st;
int gr[MAXN], k, n, m;

void read() {
    fin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int x, y;
        fin >> x >> y;
        graph[x].pb(k);
        graph[y].pb(k);
        edges[k++] = {x, y, false};
        ++gr[x];
        ++gr[y];
    }
}

bool isEulerian() {
    for (int i = 1; i <= n; ++i)
        if (gr[i] & 1)
            return 0;
    return 1;
}

void solve() {
    st.push(1);
    while (!st.empty()) {
        int node = st.top();
        if (graph[node].size() == 0) {
            st.pop();
            if (!st.empty())
                fout << node << ' ';
            continue;
        }
        int last = graph[node].back();
        int from = edges[last].from, to = edges[last].to;
        bool vis = edges[last].vis;
        graph[node].pop_back();
        if (vis == true)
            continue;
        if (from != node)
            swap(from, to);
        st.push(to);
        edges[last].vis = true;
    }
}

int main() {
    read();
    if (isEulerian() == false) {
        fout << -1;
        return 0;
    }
    solve();
    return 0;
}