#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100001
#define MMAX 500001
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m, x, y, g[NMAX], p[NMAX];
bool viz[MMAX];
vector<pair<int, int>> l[NMAX];
stack<int> st;
vector<int> sol;
int main() {
	fin >> n >> m;
	for (int i = 1; i <= m; i++) {
		fin >> x >> y;
		l[x].push_back({y, i});
		l[y].push_back({x, i});
		g[x]++;
		g[y]++;
	}
	for (int i = 1; i <= n; i++)
		if (g[i] % 2 != 0) {
			fout << -1;
			return 0;
		}
	st.push(1);
	while (!st.empty()) {
		int nod = st.top();
		if (g[nod] == 0) {
			st.pop();
			sol.push_back(nod);
			continue;
		}
		for (int i = p[nod]; i < l[nod].size(); i++) {
			int vec = l[nod][i].first;
			int mch = l[nod][i].second;
			if (!viz[mch]) {
				st.push(vec);
				viz[mch] = true;
				g[nod]--;
				g[vec]--;
				p[nod] = i + 1;
				break;
			}
		}
	}
	for (int i = 0; i < sol.size() - 1; i++)
		fout << sol[i] << " ";
	return 0;
}