#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;

inline int next_int() {
	int d;
	scanf("%d", &d);
	return d;
}

const int V = 100000 + 1;
const int E = 500000 + 500000;

int deg[V], root[V], seen[E];
int ec, eb[V], en[E], ef[E], et[E];
vector<int> tour;

void add_edge(int u, int v) {
	ef[ec] = u;
	et[ec] = v;
	en[ec] = eb[u];
	eb[u] = ec++;
}

int find(int u) {
	return (root[u] == u) ? (u) : (root[u] = find(root[u]));
}

void merge(int u, int v) {
	root[find(u)] = find(v);
}

void find_euler_tour(int u) {
	tour.push_back(u);
	for (int e = eb[u]; e != -1; e = en[e]) {
		if (seen[e] == false) {
			seen[e ^ 0] = seen[e ^ 1] = true;
			find_euler_tour(et[e]);
		}
	}
}

int main() {
	int n = next_int();
	int m = next_int();
	for (int i = 1; i <= n; i++) {
		root[i] = i;
		eb[i] = -1;
	}
	for (int i = 0; i < m; i++) {
		int u = next_int();
		int v = next_int();
		deg[u]++;
		deg[v]++;
		add_edge(u, v);
		add_edge(v, u);
		merge(u, v);
	}
	int ok = true;
	for (int i = 1; i <= n; i++) {
		if ((deg[i] & 1) || find(i) != find(1)) {
			ok = false;
		}
	}
	if (ok) {
		find_euler_tour(1);
		for (size_t i = 1; i < tour.size(); i++) {
			printf("%d ", tour[i]);
		}
	} else {
		printf("-1");
	}
	return 0;
}