#include<fstream.h>
int 
ifstream f ("");
ofstream g ("");
void citire(){
	f>>N>>M;
	for(int i=1;i<=M;i++)
	{
		f>>x>>y;
		grad[x]++;
		
		p=new nod;
		p->inf=y;
		p->adr=A[x];
		A[x]=p;
		q=new nod;
		q->inf=x;
		q->adr=A[y];
		A[y]=q;
	}
}	
void ver()
{
	for(i=1;i<=N;i++)
		if (grad [i]%2!=0)
			{ok=1;
			g<<-1;
			break;
			}

}
caut
int main (){
	citire();
	ver();
	k=1;E[k]=1;
	while(k && !ok)
	{
		x=caut(E[k]);		
		if(x)
		{	
			E[++k]=x;
			sterg(x);
		}
		else
		{
			g<<E[k];
			k--;
		}
	}







return 0;
}