#include<fstream>
#include<vector>
using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
const int N=100020;
vector<int>a[N];
vector<int>poz[N];
vector<bool>folosit[N];
int m,n,v[N],nr,x,y,st[500010];
void read()
{
	int x,y,i;
	in>>n>>m;
	for(i=0;i<m;i++)
	{
		in>>x>>y;
		a[x].push_back(y);
		a[y].push_back(x);
		poz[x].push_back(a[y].size()-1);
		poz[y].push_back(a[x].size()-1);
		folosit[x].push_back(false);
		folosit[y].push_back(false);
	}
}
int c[N],start[N];
bool viz[N];
void bfs()
{
	int i,r,u,p;
	u=p=0;
	c[p]=1;
	viz[1]=1;
	while(p<=u)
	{
		r=c[p];
		for(int i=0;i<a[r].size();i++)
		{
			y=a[r][i];
			if(!viz[y])
			{
				c[++u]=y;
				viz[y]=1;
			}
		}
		++p;
	}
	for(int i=1;i<=n;i++)
		if(!viz[i] || a[i].size()%2==1)
		{
			out<<-1;
			exit(0);
		}
}
void euler(int x)
{
	
	for(int i=0;i<a[x].size();i++)
	{
		if(folosit[x][i])
			continue;
		y=a[x][i];
		folosit[x][i]=1;
		folosit[y][poz[x][i]]=1;
		euler(y);
	}
	//if(nr<=n+1)
	v[++nr]=x;
}
void euler2()
{
	int vf=0;
	//int x,y;
	bool ok;
	x=1;
	//v[++nr]=1;
	st[++vf] = 1;
	while(vf != 0)
	{
		ok = false;
		for(int i=start[x];i<a[x].size();i++)
		{
			if(folosit[x][i])
				continue;
			y=a[x][i];
			start[x] = i+1;
			folosit[x][i]=1;
			folosit[y][poz[x][i]]=1;
			ok = true;
			break;
		}
		if(!ok)
		{
			v[++nr] = x;
			--vf;
		}
		//v[++nr]=y;
		else
			st[++vf] = y;
		x=st[vf];
	}
}
void afis()
{
	for(int i=1;i<nr;i++)
		out<<v[i]<<" ";
}
int main()
{
	read();
	bfs();
	euler2();
	afis();
	return 0;
}