#include <iostream>
#include <queue>
#include <fstream>
#include <map>
#include <set>
#include <cstring>
#include <stack>
#include <ctime>
#include <cstdlib>
#define N_MAX 100005
#define MOD 666013
using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
int n, m;
multiset<int> edges[N_MAX];
vector<int> ciclu;

stack<int> nodes;

int main()
{
    in >> n >> m;
    int x, y;
    for (int i = 1; i <= m; i++) {
        in >> x >> y;
        edges[x].insert(y);
        edges[y].insert(x);
    }
    for (int i = 1; i <= n;i++) {
        if (edges[i].size()%2!=0) {
            cout << edges[i].size();
            out << -1;
            return 0;
        }
    }
    nodes.push(1);
    while (!nodes.empty()) {
        int nod = nodes.top();
        if (edges[nod].empty()) {
            ciclu.push_back(nod);
            nodes.pop();
            continue;
        }
        int vecin = *(edges[nod].begin());
        edges[nod].erase(vecin);
        edges[vecin].erase(nod);
        nodes.push(vecin);
    }
    for (auto i : edges) {
        if (!i.empty()) {
            out << -1;
            return 0;
        }
    }
    for (int s : ciclu) {
        out << s << ' ';
    }

    return 0;
}