#include <algorithm>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <cstring>
#include <bitset>

using namespace std;

//#include <iostream>
#include <fstream>

//ifstream cin ("input.in"); ofstream cout ("output.out");

ifstream cin ("ciclueuler.in"); ofstream cout ("ciclueuler.out");

static const int NMAX = 1e5+5;
static const int MMAX = 5e5+5;

int sol[MMAX];
bitset <MMAX> f;
vector <pair<int, int>> graph[NMAX];

int k = 0;
void getEuler ( int vertex ) {
	stack <int> nodes;

	nodes.push(vertex);

	while ( nodes.size() ) {
		int curVertex = nodes.top();

		if ( !graph[curVertex].size() ) {
			sol[++k] = curVertex;
			nodes.pop();
			continue;
		}

		int edge = graph[curVertex].back().first;
		int node = graph[curVertex].back().second;
		graph[curVertex].pop_back();

		if ( !f[edge] ) {
			nodes.push(node);
			f[edge] = 1;
		}
	}
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);

	int n, m;

	cin>>n>>m;
	for ( int i = 1; i <= m; ++i ) {
		int x, y;
		cin>>x>>y;

		graph[x].push_back({i, y});
		graph[y].push_back({i, x});
	}

	for ( int i = 1; i <= n; ++i ) {
		if ( !graph[i].size() || graph[i].size()&1 ) {
			cout<<-1<<'\n';
			return 0;
		}
	}

	getEuler(1);

	for ( int i = 1; i < k; ++i ) {
		cout<<sol[i]<<" ";
	}
}