#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define lsb(x) (x & (-x))

using namespace std;


int main() {
#ifdef HOME
	ifstream cin("C.in");
	ofstream cout("C.out");
#endif
	ifstream cin("ciclueuler.in");
	ofstream cout("ciclueuler.out");
	int i, n, m;
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);

	cin >> n >> m;
	vector <vector <pair <int, int>>> g(n + 1);
	for(i = 1; i <= m; i++) {
		int x, y; cin >> x >> y;
		g[x].push_back({y, i});
		g[y].push_back({x, i});
	}
	for(i = 1; i <= n; i++) {
		if(g[i].size() & 1) {
			cout << -1;
			return 0;
		}
	}
	vector <bool> vis(m + 1);
	vector <int> sol;
	stack <int> stk;
	stk.push(1);
	while(stk.size()) {
		int nod = stk.top();
		while(g[nod].size() && vis[g[nod].back().second]) {
			g[nod].pop_back();
		}
		if(g[nod].size()) {
			stk.push(g[nod].back().first);
			vis[g[nod].back().second] = 1;
		}
		else {
			sol.push_back(nod);
			stk.pop();
		}
	}
	sol.pop_back();
	for(auto it : sol) {
		cout << it << " ";
	}

	return 0;
}