#include<bits/stdc++.h>

using namespace std;


int const MAXSIZE = 100010;
int const MAXM = 500010;

int n, m, x, y;
vector<int> ans;
vector<int> graph[MAXSIZE];
stack<int> st;

int solve () {
    st.push(1);
    while (!st.empty()) {
        int node = st.top();
        if (graph[node].size() != 0) {
            int adj = graph[node].back();
            graph[node].pop_back();
            int aux = 0;
            for (int i = 0; i < graph[adj].size(); i++) {
                if (graph[adj][i] == node && aux == 0) {
                    graph[adj].erase(graph[adj].begin() + i);
                    aux++;
                }
            }
            st.push(adj);
        } else {
            ans.push_back(node);
            st.pop();
        }
    }

}

int main () {
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= m; i++) {
        scanf("%d %d", &x, &y);
        graph[x].push_back(y);
        graph[y].push_back(x);
    }
    for (int i = 1; i <= n; i++) {
        if (graph[i].size() % 2) {
            printf("-1 ");
            return 0;
        }
    }
    solve();
    for (int i = 0; i < ans.size() - 1; i++)
        printf("%d ", ans[i]);
}