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

const int NMAX = 100000;
const int MMAX = 500000;

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] != -1) {
			const int to = E[idx] ^ node;
			E[idx] = -1;
			fout << node + 1 << ' ';
			dfs(to, fout);
		}
	}
}

int main() {
	ifstream fin("ciclueuler.in");
	ofstream fout("ciclueuler.out");
	fin.tie(0);
	ios_base::sync_with_stdio(false);

	int n, m; fin >> n >> m;
	for (int i = 0; i < m; i++) {
		int x, y; fin >> 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) {
			fout << "-1\n";
			return 0;
		}
	}

	dfs(0, fout);
	fout << "1\n";
	return 0;
}