#include<fstream>
#include<list>
#include<stack>
#include<bitset>
 
using namespace std;
 
const int Nmax = 100001;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

list<int> G[Nmax], output;
stack<int> st;
bitset<Nmax> viz;
int N, M, deg[Nmax], ok = 1;
 
void DFS(int nod) {
    viz[nod] = 1;
    for(auto it=G[nod].begin(); it!=G[nod].end(); ++it)
        if(!viz[*it])
            DFS(*it);
}
 
void remove_node(int from, int to) {
    deg[from]--, deg[to]--;
    G[from].pop_front();
    for(auto it=G[to].begin(); it!=G[to].end(); ++it)
        if(*it == from) {
            G[to].erase(it);
            break;
        }
}
 
void euler(int node) {
    while(1) {
        if(G[node].empty() == true)
            break;
        st.push(node);
        int new_node = G[node].front();
        remove_node(node, new_node);
        node = new_node;
    }
}

void make_euler_cycle() {
	int node = 1;
    do {
        euler(node);
        node = st.top();
        st.pop();
        output.push_back(node);
    } while(!st.empty());
}

void read_data() {
	
	int to, from;

	f >> N >> M;

    while(M--) {
        f >> to >> from;
        G[to].push_back(from);
        G[from].push_back(to);
        deg[to]++;
		deg[from]++;
    }
}

bool are_degrees_odd() {
	for(int i=1; i<=N; i++)
        if(deg[i]%2 == 1) 
			return false;
	return true;
}
        
bool is_graph_connected() {
	DFS(1);
    for(int i=1; i<=N; i++)
		if(!viz[i]) 
			return false;
	return true;
}

int main() {

	read_data();
 
	if(is_graph_connected() && are_degrees_odd()) {
		make_euler_cycle();
		for(auto it=output.begin(); it!=output.end(); ++it)
			g << *it << " ";
	}
	else
		g << -1;

	f.close();
	g.close();
 
    return 0;
}