#include <iostream>
#include <fstream>
#include <vector>

#define IN_FILE "ciclueuler.in"
#define OUT_FILE "ciclueuler.out"

std::ifstream fin(IN_FILE);
std::ofstream fout(OUT_FILE);

#define MAX_N 100005
#define MAX_M 500005

struct Node {
    int num;
    int id;
};

int n, m;
std::vector<Node> graph[MAX_N];
bool visited[MAX_M];
std::vector<int> eulerCycle;

int GetNextEdge(int node) {
    while (!graph[node].empty() && visited[graph[node].back().id]) {
        graph[node].pop_back();
    }
    if (graph[node].empty()) {
        return 0;
    }
    Node nextNode = graph[node].back();
    visited[nextNode.id] = true;
    return nextNode.num;
}

void RecursiveEulerCycleBuilder(int node) {
    while (int destNode = GetNextEdge(node)) {
        RecursiveEulerCycleBuilder(destNode);
    }
    eulerCycle.push_back(node);
}

int main() {
    fin >> n >> m;
    
    int a, b;
    for (int i = 0; i < m; i++) {
        fin >> a >> b;
        graph[a].push_back({b, i});
        graph[b].push_back({a, i});
    }

    for (int i = 0 ; i < n; i++) {
        if (graph[i].size() % 2) {
            fout << -1 << '\n';
            return 0;
        }
    }

    RecursiveEulerCycleBuilder(1);

    for (int x : eulerCycle) {
        fout << x << ' ';
    }
    fout << '\n';
}