#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define N 100003
#define M 500004
using namespace std;
int usedEdge[M],from[M],to[M],n,m;
vector<int> G[N],sol;
int dfs();
int main() {
	ifstream fin("ciclueuler.in");
	ofstream fout("ciclueuler.out");
	fin >> n >> m;
	int x, y;
	for (int i = 1; i <= m; i++) {
		fin >> x >> y;
		from[i] = x; to[i] = y;
		G[x].push_back(i); G[y].push_back(i);
	}
	for (int i = 1; i <= n; i++) {
		if (G[i].size() % 2 != 0) {
			fout << "-1";
			return 0;
		}
	}
	dfs();
	for (int i = 0; i < sol.size(); i++) {
		fout << sol[i] << " ";
	}
}
int dfs() {
	vector<int> nodesStack;
	nodesStack.push_back(1);
	
	while (!nodesStack.empty()) {
		int frontNode = nodesStack.back();
		//cout << "front" << frontNode <<endl;
		if (!G[frontNode].empty()) {
			int edge = G[frontNode].back();
			G[frontNode].pop_back();
			if (usedEdge[edge] != 1) {
				usedEdge[edge] = 1;
				int nodePushed = from[edge] != frontNode ? from[edge] : to[edge];
				nodesStack.push_back(nodePushed);
			}
		} else {
			//cout<< "rest" << frontNode<<endl;
			sol.push_back(frontNode);
			nodesStack.pop_back();
		}
	}
}