#include <fstream>
#include <queue>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

struct edge{
    int a, b;
};

vector<int> adj[int(1e5) + 5];
edge edges[int(5e5) + 5];
int bye[int(5e5) + 5];

vector<int> results;

int get_next_edge(int node){

    while (adj[node].size() && bye[adj[node].back()])
        adj[node].pop_back();

    if (adj[node].empty())
        return 0;

    int edgeId = adj[node].back();
    bye[edgeId] = true;
    return edges[edgeId].a + edges[edgeId].b - node;

}

void euler(int node){

    while (int vec = get_next_edge(node)){
        euler(vec);
    }
    results.push_back(node);

}

int main(){
    int n, m;
    fin >> n >> m;
    for (int edgeId = 1; edgeId <= m; edgeId++){
        int a, b;
        fin >> a >> b;
        edges[edgeId].a = a;
        edges[edgeId].b = b;
        adj[a].push_back(edgeId);
        adj[b].push_back(edgeId);
    }

    for (int node = 1; node <= n; node++){
        if (adj[node].size() % 2) {
            fout << -1;
            return 0;
        }
    }

    euler(1);

    results.pop_back();
    for (int node: results)
        fout << node << " ";
    return 0;
}