#include <list>
#include <fstream>
#include <vector>
#include <iostream>
#include <algorithm>
#include <queue>
#include <stack>
using namespace std;

queue <int> Q;
vector <bool> viz;
vector <int> G;
stack <int> sol;
vector <list <int> > g;
int n, m;
bool res = 1;

ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

void bfs(int x) {
    Q.push(x);
    viz[x] = 1;
    while (Q.size()) {
        x = Q.front();
        Q.pop();
        for (list <int> :: iterator it = g[x].begin(); it != g[x].end(); ++it)
            if (!viz[*it]) {
                viz[*it] = 1;
                Q.push(*it);
            }
    }
}

bool grad() {
    for (int i = 1; i <= n; ++i)
        if (G[i] & 1 || (!viz[i] && G[i]))
            return 0;
    return 1;
}

void euler(int x) {
    sol.push(x);
    while (sol.size()) {
        x = sol.top();
        if (!g[x].size()) {
            fout << x << " ";
            sol.pop();
        }
        else {
            int y = *g[x].begin();
            g[x].erase(g[x].begin());
            list <int> :: iterator it = g[y].begin();
            while (it != g[y].end() && *it != x)
                ++it;
            g[y].erase (it);
            sol.push(y);
        }
    }
}

int main() {
    fin >> n >> m;
    viz.resize(n+1);
    G.resize(n+1);
    g.resize(n+1);
    while (m--) {
        int x, y;
        fin >> x >> y;
        if (x != y)
            G[x]++, G[y]++;
        g[x].push_back (y);
        g[y].push_back (x);
    }
    fin.close();
    bfs(1);
    res = grad();
    if (res)
        euler(1);
    else
        fout << -1;
    fout.close();
}