#include <fstream>
#include <vector>
#include <stack>
#include <list>
#include <algorithm>
#include <queue>

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

vector <int> rasp;
list <int> ls[100005];
int n, m, x, y, i, l;
bool viz[100005];
stack<int>stiva;

int main() {
    f >> n >> m;
    while (m--) {
        f >> x >> y;
        ls[x].push_back(y);
        ls[y].push_back(x);
    }

    for (i = 1; i <= n; i++)
        if (ls[i].size()%2 == 1 || ls[i].size() == 0) {
            g << "-1";
            return 0;
        }
    stiva.push(1);
    while (stiva.empty()==0) {
        x = stiva.top();
        while (ls[x].size()) {
            y = ls[x].front();
            stiva.push(y);
            ls[x].pop_front();
            ls[y].erase(find(ls[y].begin(),ls[y].end(), x));
            x = y;
        }
        rasp.push_back(stiva.top());
        stiva.pop();
    }
    vector<int>::iterator it;
    for(it = rasp.begin(); it != rasp.end(); it++)
        g << *it << ' ';

    return 0;
}