#pragma GCC optimize("O3")
#include<bits/stdc++.h>
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define in insert
#define er erase
#define fd find
#define fr first
#define sc second
typedef long long ll;
typedef long double ld;
const ll INF=0x3f3f3f3f3f3f3f3f;
const ll llinf=(1LL<<62);
const int inf=(1<<30);
const int nmax=1e5+50;
const int mod=1e9+7;
using namespace std;
int n,m,i,j,x,y,nr,viz[nmax],dg[nmax];
vector<int>vc,ans;
vector<pair<int,int> >a[nmax];
stack<int>q;
int main()
{
	freopen("ciclueuler.in","r",stdin);
	freopen("ciclueuler.out","w",stdout);
	//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
	ios_base::sync_with_stdio(false);cin.tie(0);cerr.tie(0);cout.tie(0);
	cin>>n>>m;
	for(i=1;i<=m;i++)
	{
		cin>>x>>y;
		nr++;
		a[x].pb({y,nr});
		a[y].pb({x,nr});
	}
	for(i=1;i<=n;i++)
	{
		if((int)a[i].size()&1)rc(-1);
		if((int)a[i].size())x=i;
	}
	q.push(x);
	while(!q.empty())
	{
		x=q.top();
		for(i=dg[x];i<a[x].size();i++)
		{
			if(!viz[a[x][i].sc])
			{
				viz[a[x][i].sc]=1;
				q.push(a[x][i].fr);
				break;
			}
		}
		dg[x]=i;
		if(dg[x]==(int)a[x].size())
		{
			q.pop();
			ans.pb(x);
		}
	}
	for(i=1;i<=nr;i++)if(!viz[i])rc(-1);
	for(i=0;i<(int)ans.size()-1;i++)cout<<ans[i]<<" ";
	cout<<endl;
    return 0;
}