#include <fstream>
#include <vector>
#include <stack>
#include <list>
using namespace std;
ifstream ka("ciclueuler.in");
ofstream ki("ciclueuler.out");

const int N_MAX = 100000;
const int M_MAX = 500000;

list <int> muchii[N_MAX + 1];
bool folosita[M_MAX + 1], vazut[N_MAX + 1];
int grad[N_MAX + 1];
stack <int> stiva;
vector <int> raspuns;

void sterge(int x, int y)
{
    muchii[x].pop_front();
    for(list<int>::iterator it = muchii[y].begin(); it != muchii[y].end(); ++it)
        if(*it == x)
        {
            muchii[y].erase(it);
            break;
        }
}

int n, m;
int main()
{
    ka >> n >> m;
    int x, y;
    for(int i = 1; i <= m; i++)
    {
        ka >> x >> y;
        muchii[x].push_back(y);
        muchii[y].push_back(x);
        grad[x]++;
        grad[y]++;
    }
    stiva.push(x);
    while(!stiva.empty())
    {
        int curent = stiva.top();
        vazut[curent] = true;
        stiva.pop();
        if(!muchii[curent].empty())
        {
            stiva.push(curent);
            stiva.push(muchii[curent].front());
            sterge(curent, muchii[curent].front());
            raspuns.push_back(curent);
        }
    }
    bool euler = true;
    for(int i = 1; i <= n && euler; i++)
    {
        if(!vazut[i] || grad[i] % 2 != 0)
            euler = false;
    }
    if(euler)
        for(int i = 0; i < raspuns.size(); i++)
            ki << raspuns[i] << " ";
    else
        ki << -1;
}