#include <bits/stdc++.h>
using namespace std;
 
typedef int ll;
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define pi pair<ll, ll>
#define sz(x) (int)((x).size())
#define all(a) (a).begin(), (a).end()

/* int f[maxn],nf[maxn],inv[maxn];
const int M=998244353;
void init(){
    inv[1]=1; for (int i=2;i<maxn;i++) inv[i]=M-1ll*(M/i)*inv[M%i]%M;
    f[0]=nf[0]=1; for (int i=1;i<maxn;i++) f[i]=1ll*f[i-1]*i%M,nf[i]=1ll*nf[i-1]*inv[i]%M;
}
int C(int x,int y){return 1ll*f[x]*nf[y]%M*nf[x-y]%M;}*/
const ll mod = 1e9+7;
ll n, k, m, mi, ma;
const ll N = 5e5 + 25;
vector<bool> v(N, 0);
vector<pi> a[N/5];

vector<ll> ans;

void dfs(ll x){
	while(!a[x].empty()){
		pi r = a[x].back();
		a[x].pop_back();
		if(v[r.s]) continue;
		v[r.s] = 1;
		dfs(r.f);
		ans.pb(x + 1);
		return;
	}
}

void solve(){
	
	ifstream cin("ciclueuler.in");
	ofstream cout("ciclueuler.out");
	
	cin >> n >> m;
	
	for(int i = 0; i<m; i++){
		ll x, y;
		cin >> x >> y;
		x--; y--;
		a[x].pb({y, i});
		a[y].pb({x, i});
	}
	for(int i = 0; i < n; i++) if(a[i].size()%2) {
		cout << "-1\n";
		return;
	}
	dfs(0);
	for(int i = 0; i<ans.size(); i++) {
		cout << ans[i] << " ";
	}

}

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int t=1;
//	cin >> t;
	while(t--) solve();
	
	return 0;
}