#include <iostream>
#include <fstream>
#include <vector>
 
using namespace std;
 
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

#define MAXN 500005

struct muchie
{
    int x,y;
    bool viz;
}e[MAXN];
 
int n,m;
vector<int> g[MAXN];
 
int Check()
{
    for(int i = 1; i <= n; i++)
        if (g[i].size() % 2 != 0)
            return 0;

    return 1;
}

void Euler(int node){
    while(!g[node].empty()){

        int i = g[node].back();
        g[node].pop_back();

        if(!e[i].viz){
            int next = e[i].x + e[i].y - node;
            e[i].viz = true;

            Euler(next);
        }
    }
    cout << node << " ";
}

int main()
{
    cin >> n >> m;

    for (int i = 1; i <= m; i++)
    {
        cin >> e[i].x >> e[i].y;
        g[e[i].x].push_back(i);
        g[e[i].y].push_back(i);
    }

    if (Check())
        Euler(1);
    else
        cout << -1;

    return 0;
}