#include <algorithm>
#include <fstream>
#include <vector>
#define SZ(x) ((int) (x).size())
using namespace std;

const int NMAX = 100005, MMAX = 500005;

vector<int> G[NMAX];

bool usedEdge[MMAX];
int from[MMAX], to[MMAX];

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

    int n, m;
    fin >> n >> m;

    for (int i = 0; i < m; ++i) {
        int x, y;
        fin >> x >> y;
        G[x].push_back(i);
        G[y].push_back(i);
        from[i] = x;
        to[i] = y;
    }

    for (int i = 1; i <= n; ++i) {
        if (SZ(G[i]) & 1) {
            fout << "-1\n";
            return 0;
        }
    }

    vector<int> ans;

    vector<int> stk;
    stk.push_back(1);
    while (!stk.empty()) {
        int node = stk.back();
        if (!G[node].empty()) {
            int e = G[node].back();
            G[node].pop_back();
            if (!usedEdge[e]) {
                usedEdge[e] = true;
                int to = ::from[e] ^ ::to[e] ^ node;
                stk.push_back(to);
            }
        } else {
            stk.pop_back();
            ans.push_back(node);
        }
    }

    for (int i = 0; i < SZ(ans) - 1; ++i) {
        fout << ans[i] << ' ';
    }
    fout << '\n';

    fin.close();
    fout.close();
}