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