#include <bits/stdc++.h>
#define Nmax 100005
using namespace std;


int N, M;
set<int> S[Nmax];
vector<int> ans;

void Euler(int node) {
    ans.push_back(node);
    if (S[node].size() == 0) return;
    else {
        int nxt = *S[node].begin();
        S[nxt].erase(S[nxt].find(node));
        S[node].erase(S[node].begin());
        Euler(nxt);
    }
}
int main()
{
    ifstream fin("ciclueuler.in");
    ofstream fout("ciclueuler.out");

    fin >> N >> M;
    for (int i = 1; i <= M; ++i) {
        int x, y;
        fin >> x >> y;
        S[x].insert(y);
        S[y].insert(x);
    }


    for (int i = 1; i <= N; ++i)
    if (S[i].size() % 2) {
        fout << -1;
        return 0;
    }

    Euler(1);
    ans.pop_back();
    for (auto it: ans)
        fout << it << " ";


    return 0;
}