#include <stdio.h>
#include <list>
#include <vector>
#include <queue>
#include <stack>
using namespace std;

#define Nmax 100005

vector<list<int>> Graph;
list<int> sol;
stack<int> s;
int deg[Nmax];
int visited[Nmax];
int n, m;

void read(){
    int u, v;
    scanf("%d %d", &n, &m);
    Graph.resize(n + 1);
    while (m--){
        scanf("%d %d", &u, &v);
        Graph[u].push_back(v);
        Graph[v].push_back(u);
        ++deg[u];
        ++deg[v];
    }
}

void bfs(int v){
    queue<int> q;
    q.push(v);
    visited[v] = 1;

    while (!q.empty()){
        v = q.front();
        q.pop();
        for (list<int>::iterator it = Graph[v].begin(); it != Graph[v].end(); ++it)
            if (!visited[*it]){
                q.push(*it);
                visited[*it] = 1;
            }
    }
}

void delete_edge(int u, int v){
    Graph[u].pop_front();
    for (list<int>::iterator it = Graph[v].begin(); it != Graph[v].end(); ++it)
        if (*it == u){
            Graph[v].erase(it);
            break;
        }
}

int is_euler(){
    int v, u;
    bfs(1);
    for (int i = 1; i <= n; ++i)
        if (!visited[i] || deg[i] % 2 == 1)
            return 0;
    
    s.push(1);
    while (!s.empty()){
        v = s.top();
        while (!Graph[v].empty()){
            u = Graph[v].front();
            s.push(u);
            delete_edge(v, u);
            v = u;
        }
        v = s.top();
        s.pop();
        sol.push_back(v);
    }
    return 1;
}

int main(){
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    read();
    if ( is_euler() ){
        sol.pop_back();
        for (list<int>::iterator it = sol.begin(); it != sol.end(); ++it)
            printf("%d ", *it);
    }
    else
        printf("-1\n");
    return 0;
}