#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

#define NMax 100010
#define MMax 500010

int n, m;
vector<int> G[NMax];
int from[MMax], to[MMax];
vector<bool> viz(MMax, false);

stack<int> s;
vector<int> rez;

void init();
void rezolvare();

int main(){
	init();
	rezolvare();
}

void init(){
	int i, x, y;
	fin >> n >> m;
	for(i = 1; i <= m; i++){
		fin >> x >> y;
		G[x].push_back(i);
		G[y].push_back(i);
		from[i] = x;
		to[i] = y;
	}
}

void rezolvare(){
	int i, x, y, e;
	
	for(i = 1; i <= n; i++)
		if(G[i].size() & 1){
			fout << -1;
			return;
		}
	
	s.push(1);
	while(s.size()){
		x = s.top();
		if(G[x].size()){
			e = G[x].back();
			G[x].pop_back();
			if(!viz[e]){
				viz[e] = true;
				y = to[e] ^ from[e] ^ x;
				s.push(y);
			}
		}
		else{
			s.pop();
			rez.push_back(x);
		}
	}
	for(i = 0; i < rez.size() - 1; i++) fout << rez[i] << ' ';
}