#include <fstream>
#include <vector>

using namespace std;

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

const int N = 1e5 + 1;
const int M = 5e5 + 1;

struct edge
{
    int u,v;
    bool vis;
};

edge e[M];

bool ok;

vector<int> v[N];

void euler(int x) {
    while (v[x].size() != 0)
        {
        int cur = v[x].back();
        v[x].pop_back();
        if (e[cur].vis) continue;
        e[cur].vis = 1;
        int next = (x ^ e[cur].u ^ e[cur].v);
        euler(next);

    }
    if (ok) out << x << " ";
    ok = 1;
}

int main()
{
    int n,m;
    in >> n >> m;
    for (int i = 1; i <= m; i++) {
        in >> e[i].u >> e[i].v;
        v[e[i].u].push_back(i);
        v[e[i].v].push_back(i);
    }
    bool pos =1;
    for (int i = 1; i <= n; i++)
    {
        if (v[i].size()%2)
        {
            pos = 0;
        }
    }
    if (!pos) out << -1;
    else euler(1);
    return 0;
}