#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
int j,l,v1,x,y,i,n,m,val,u,nr;
vector < int > v;
vector < int > h[100002];
vector < int >::iterator it;
char a[40];
int main()
{
freopen("ciclueuler.in","r",stdin);
freopen("ciclueuler.out","w",stdout);
scanf("%d",&n);
scanf("%d\n",&m);
for(i=1;i<=m;i++)
{
	//scanf("%d",&x);
	//scanf("%d",&y);
	gets(a);
	l=strlen(a)-1;
	x=0;
	for(j=0;a[j]!=' ';j++)
		x=x*10+a[j]-48;
	y=0;
	for(j=j+1;j<=l;j++)
		y=y*10+a[j]-48;
	h[x].push_back(y);
	h[y].push_back(x);
}
for(i=1;i<=n;i++)
	if(h[i].size()%2==1)
	{
		printf("-1\n");
		return 0;
	}
u=1;
v.push_back(1);
nr=0;
while(u>0)
{
	if(nr==m) return 0;
	if(h[v[u-1]].size()==0)
	{
		printf("%d ",v[u-1]);
		u--;
		v.erase(v.begin()+u);
	}
	else
	{
		v1=v[u-1];
		val=h[v1][0];
		h[v1].erase(h[v1].begin());
		for(it=h[val].begin();it!=h[val].end();it++)
			if(*it==v1)
			{
				h[val].erase(it);
				break;
			}
		u++;
		v.push_back(val);
	}
}
return 0;
}