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

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

const int maxn = 1e5 + 5;
const int maxm = 5e5 + 5;
vector <pair <int,int> > G[maxn];
bitset <maxm> Vis;

bool Is_Euler (int n) {
    for (int  i = 1; i <= n; i++) {
        if (G[i].size() & 1) return false;
    }
    return true;
}

void Euler () {
    stack <int> Stk;
    int node, son, edge;
    Stk.push(1);
    while (!Stk.empty()) {
        node = Stk.top();
        if (G[node].empty()) {
            fout << node << " ";
            Stk.pop();
        } else {
            son = G[node][0].first;
            edge = G[node][0].second;
            G[node].erase(G[node].begin());
            if (Vis[edge] == false) {
                Vis[edge] = true;
                Stk.push(son);
            }

        }
    }
}

int main() {
    ios_base :: sync_with_stdio (false);
    int n, m, x, y, i;
    fin >> n >> m;
    for (i = 1; i <= m; i++) {
        fin >> x >> y;
        G[x].push_back(make_pair(y, i));
        G[y].push_back(make_pair(x, i));
    }
    if (!Is_Euler(n)) {
        fout << "-1\n";
    } else {
        Euler();
        fout << "\n";
    }
    fin.close();
    fout.close();
    return 0;
}