#include <iostream>
#include <fstream>
#include <vector>
#include <set>
#define nmax 100005
#define mmax 500005
using namespace std;

multiset <int> v[nmax];
vector <int> sol;
int n, m, a, b, deg[nmax];
bool has = true;

void euler(int x) {
	while(!v[x].empty()) {
		int w = *v[x].begin();
		v[x].erase(v[x].begin());
		v[w].erase(v[w].find(x));
		euler(w);
	}
	sol.push_back(x);
}
		

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

	f>>n>>m;
	for(int i=1; i<=m; i++) {
		f>>a>>b;
		deg[a]++;
		deg[b]++;
		v[a].insert(b);
		v[b].insert(a);
	}
	for(int i=1; i<=n; i++) if(deg[i] % 2 == 1) has = false;

	if(has) {
		euler(1);
		for(int i=0; i<sol.size(); i++) g<<sol[i]<<" ";
		g<<"\n";
	}
	else g<<"-1\n";
	
	return 0;
}