#include<stdio.h>
#include<vector>
#define input "ciclueuler.in"
#define output "ciclueuler.out"
using namespace std;
const int N=500001;
int n,x,y,i,m;
int ce[N],nrm;
vector<int> a[N];
vector<pair<int,int> > muchii;
vector<bool> marcat;

void read()
{
	scanf("%d %d", &m,&n);
	for(i=1;i<=m;i++)
	{
		scanf("%d %d",&x,&y);
		muchii.push_back(make_pair(x,y));
		marcat.push_back(false);
		a[x].push_back(i);
		a[y].push_back(i);
	}
}
inline int nod(int nrm,int x)
{
	if (muchii[nrm].first==x)
		return muchii[nrm].second;
	return muchii[nrm].first;
}
void euler(int x)
{
	int y,i;
	for(i=0;i<a[x].size();i++)
	{
		nrm=a[x][i];
		if (marcat[nrm])
			continue;
		y=nod(nrm,x);
		marcat[y]=true;
		euler(y);
	}
	ce[nrm++]=x;
}

void open()
{
	freopen(input,"r",stdin);
	freopen(output,"w",stdout);
}

void _where_the_magic_begins()
{
	for (int i=1;i<=n;i++)
		if (a[i].size()%2)
		{
			printf("-1\n");
			return;
		}
	
	euler(1);
	if(nrm!=m+1 || ce[1]!=1)
	{
		printf("-1\n");
		return;
	}
	for (int i=nrm;i>1;i--)
		printf("%d ",ce[i]); 
    

}

int main()
{
	open();
	read();
	_where_the_magic_begins();
    return 0;
}