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

int i,j,n,m,k,x,y;
bool viz[500010];
struct vec
{
	int nod,poz;
};
vector<vec> a[100002];
void det(int x)
{
	int i;
	for(i=0;i<a[x].size();++i)
	if(!viz[a[x][i].poz])
	{
		viz[a[x][i].poz]=1;
		det(a[x][i].nod);
	}
	fprintf(g,"%d ",x);
}
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;
}