#include<fstream>
#include<vector>
using namespace std;

int i,j,n,m,k,x,y;
bool uz[500001];
struct date
{
	int nod,poz;
};
vector<date> a[100002];
int df(int x)
{
	int i;
	for(i=0;i<a[x].size();++i)
	if(!uz[a[x][i].poz])
	{
		uz[a[x][i].poz]=1;
		df(a[x][i].nod);
	}
	printf("%d ",x);
}
int main()
{
	freopen("ciclueuler.in","r",stdin);
	freopen("ciclueuler.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(i=1;i<=m;++i)
	{
		scanf("%d%d",&x,&y);
		a[x].push_back((date) {y,i});
		a[y].push_back((date) {x,i});
	
	}
	for(i=1;i<=n;++i)
		if(a[i].size()%2!=0)
		{
			printf("-1\n");
			break;
		}
		df(1);
	return 0;
}