#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");


const int MAX_N = 100100;
const int MAX_M = 500100;

int n, m;
int grade[MAX_N];

bool vis[MAX_M];

int x[MAX_M], y[MAX_M];

vector<int> g[MAX_N];


inline void euler(const int &node) {
	
	while (g[node].size()) {
		int i = g[node][g[node].size() - 1];
		
		g[node].pop_back();
		if (!vis[i]) {
			vis[i] = true;
			euler(x[i] + y[i] - node);
		}
	}
	fout << node << ' ';
}


int main() {
	fin >> n >> m;
	for (int i = 1; i <= m; ++i) {
		fin >> x[i] >> y[i];
		g[x[i]].push_back(i);
		g[y[i]].push_back(i);
		++grade[x[i]]; ++grade[y[i]];
	}
	fin.close();
	
	for (int i = 1; i <= n; ++i)
		if (grade[i] & 1) {
			fout << "-1\n";
			fout.close();
			return 0;
		}
	
	euler(1);
	fout.close();
	
}