#include <fstream>
#include <vector>
#include <queue>
#include <stack>
#define N_MAX   100001
#define M_MAX   500001

using namespace std;

int usedEdge[M_MAX], visited[N_MAX], from[N_MAX], to[N_MAX];
vector<int> G[N_MAX];

int main() {
    ifstream in("ciclueuler.in");
    int n, m;
    in >> n >> m;
    for(int i = 0; i < m; ++i){
        int x, y;
        in >> x >> y;
        from[i] = x;
        to[i] = y;
        G[x].push_back(i);
        G[y].push_back(i);
    }
    in.close();

    ofstream out("ciclueuler.out");
    for (int i = 1; i <= n; ++i) {
        if (G[i].size() % 2) {
            out << "-1\n";
            out.close();
            return 0;
        }
    }
    
    std::stack<int> s;
    std::vector<int> cycle;
    s.push(1);
    while (!s.empty()) {
        int node = s.top();
        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;
                s.push(to);
            }
        } else {
            s.pop();
            cycle.push_back(node);
        }
    }


    for(int i = 0; i < cycle.size() - 1; ++i){
        out << cycle[i] << ' ';
    }

    out.close();

    return 0;
}