#include <cassert>
#include <cstdio>
#include <cstring>
#include <stack>
#include <vector>

using namespace std;

inline int next_int() {
	int n = 0;
	char c = getchar_unlocked();
	while (!('0' <= c && c <= '9')) {
		c = getchar_unlocked();
	}
	while ('0' <= c && c <= '9') {
		n = n * 10 + c - '0';
		c = getchar_unlocked();
	}
	return n;
}

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;
stack<int> stk;

inline 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]));
}

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

inline void euler(int v) {
	while (true) {
		int c = 1;
		for (int e = eb[v]; e != -1; e = en[e]) {
			if (seen[e] == false) {
				seen[e ^ 0] = seen[e ^ 1] = true;
				stk.push(v);
				v = et[e];
				c = 0;
				break;
			}
		}
		if (c) {
			break;
		}
	}
}

inline void find_euler_tour(int v) {
	do {
		euler(v);
		v = stk.top();
		stk.pop();
		tour.push_back(v);
	} while (!stk.empty());
}

int main() {
	freopen("ciclueuler.in", "r", stdin);
	freopen("ciclueuler.out", "w", stdout);
	const int n = next_int();
	const 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 (int i = tour.size() - 1; i >= 0; i--) {
			printf("%d ", tour[i]);
		}
	} else {
		printf("-1");
	}
	return 0;
}