#include <bits/stdc++.h>

using namespace std;
typedef int var;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

#define MAXN 100005

vector<pair<int, int>> G[MAXN];
bool Viz[MAXN];
int Parent[MAXN];
bool Del[1000000];

void dfs(int node) {

	Viz[node] = 1;
	for(auto &e : G[node]) {
		if(!Viz[e.first]) {
			Parent[e.first] = node;
			Del[e.second] = 1;

			dfs(e.first);
		}
	}
}
vector<int> Ciclu;
void ciclu(int node) {

	while(node != 0) {
        Ciclu.push_back(node);

		while(!G[node].empty() && Del[G[node].back().second])
			G[node].pop_back();

		if(G[node].empty()) {
			node = Parent[node];
		} else {
			Del[G[node].back().second] = 1;
			node = G[node].back().first;
			G[node].pop_back();
		}
	}

	Ciclu.pop_back();
}

int main() {

    int m, n, a, b;
    fin>>n>>m;

    while(m--) {
        fin>>a>>b;
        G[a].push_back({b, m});
        G[b].push_back({a, m});
    }

    dfs(1);

    for(int i=1; i<=n; i++) {
        if(!Viz[i] || G[i].size() % 2) {
            fout<<"-1";
            return 0;
        }
    }

    ciclu(1);
    for(auto i : Ciclu) fout<<i<<" ";

    return 0;
}