#include <cstdio>
#include <iostream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <functional>
#include <string>
#include <cstring>
#include <cmath>
#include <map>
#include <set>
#include <bitset>
#include <stack>
#include <iomanip>
#define MOD 1000000007
#define NMAX 100005
#define INF 0x3f3f3f3f
#define pb push_back

using namespace std;

FILE *fin = freopen("ciclueuler.in", "r", stdin);
FILE *fout = freopen("ciclueuler.out", "w", stdout);

typedef pair<int, int> pii;

vector<int> v[NMAX], aux;
vector<int>::iterator it;
stack<int> st;
int nrm = 1, m;

int main() {
	int n, i, x, y, a, b;

	scanf("%d%d", &n, &m);
	for (i = 0; i < m; ++i) {
		scanf("%d%d", &x, &y);

		v[x].pb(y);
		v[y].pb(x);
	}

	for (i = 1; i <= n; ++i) {
		if (v[i].size() % 2 != 0 || v[i].empty()) {
			cout << -1;
			return 0;
		}
	}

	st.push(1);
	x = 1;
	while (!st.empty()) {
		x = st.top();

		if (v[x].size()) {
			y = v[x].back();

			v[x].erase(v[x].end() - 1);
			for (it = v[y].begin(); it != v[y].end(); ++it) {
				if (*it == x) {
					v[y].erase(it);
					break;
				}
			}

			st.push(y);
		}
		else {
			y = st.top();
			st.pop();

			if (!st.empty())
				printf("%d ", y);
		}
	}

	return 0;
}