#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>
#define Nmax 100010

using namespace std;
 
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
 
int N, M, X, Y;

vector<int> G[Nmax];
stack<int> S;
 
void stergere(int nod, int nr)
{
    for(vector<int>::iterator it = G[nod].begin(); it != G[nod].end(); ++ it)
        if(*it == nr)
        {
            G[nod].erase(it);
            return ;
        }
}
 
void Euler(int nod)
{
    S.push(nod);
	
    while(!S.empty())
    {
        int nod = S.top();
        if(G[nod].size())
        {
            int nr = G[nod].back();
            G[nod].pop_back();
            stergere(nr, nod);
            S.push(nr);
        }
		else
        {
            fout<<nod<<" ";
            S.pop();
        }
    }
}
 
int main()
{
    int i;
	
    fin>>N>>M;
	
    for(i = 1; i <= M; ++ i)
    {
        fin>>X>>Y;
        G[X].push_back(Y);
        G[Y].push_back(X);
    }
    for(i = 1; i <= N; ++ i)
        if(G[i].size() % 2)
        {
            fout<<"-1";
			return 0;
        }
    Euler(1);
	
    return 0;
}