#include <fstream>
#include <vector>
#define SZ(x) ((int) (x).size())
using namespace std;

const int NMAX = 100000, MMAX = 500000;
const int NIL = -1;

vector<int> G[NMAX];
int E[MMAX];

void dfs(const int& node, ofstream& fout) {
	while (not G[node].empty()) {
		const int idx = G[node].back();
		G[node].pop_back();
		if (E[idx] != NIL) {
			const int to = E[idx] ^ node;
			E[idx] = NIL;
			fout << 1 + node << ' ';
			dfs(to, fout);
		}
	}
}

int main(void) {
	ifstream cin("ciclueuler.in");
	ofstream cout("ciclueuler.out");
	cin.tie(0);
	ios_base::sync_with_stdio(false);

	int n, m; cin >> n >> m;
	for (int i = 0; i < m; i++) {
		int x, y; cin >> x >> y; x--; y--;
		E[i] = x ^ y;
		G[x].push_back(i);
		G[y].push_back(i);
	}
	
	for (int i = 0; i < n; i++) {
		if (SZ(G[i]) & 1) {
			cout << "-1\n";
			return 0;
		}
	}

	dfs(0, cout);
}