#include<fstream>
#include<vector>
#include<queue>
using namespace std;
FILE *g=fopen("ciclueuler.out","w");

int i,j,n,m,k,x,y;
bool viz[100002];
queue<int> q;
struct vec
{
	int nod,poz;
};
vector<vec> a[100002];
void det(int x)
{
	int i;
	q.push(x);
	while(!q.empty())
	{
		x=q.front();
			fprintf(g,"%d ",x);
	for(i=a[x].size()-1;i>=0;--i)
	if(!viz[a[x][i].poz])
	{
		//fprintf(g,"%d %d\n",a[x][i].nod,a[x][i].poz);
		viz[a[x][i].poz]=1;
		q.push(a[x][i].nod);
		//a[x].erase(a[x].begin()+i);
		break;
	}
	//fprintf(g,"%d ",q.back());
	/*if(!q.back())
	{
		if(q.size()>1)
			fprintf(g,"%d ",x);*/
	q.pop();
	//}
	}
	
}
int main()
{
	FILE *f=fopen("ciclueuler.in","r");
	fscanf(f,"%d%d",&n,&m);
	for(i=1;i<=m;++i)
	{
		fscanf(f,"%d%d",&x,&y);
		a[x].push_back((vec) {y,i});
		a[y].push_back((vec) {x,i});
	}
	for(i=1;i<=n;++i)
		if(a[i].size()%2!=0)
		{
			fprintf(g,"-1\n");
			return 0;
		}
		det(1);
	return 0;
}