# include <fstream>
using namespace std;
int n, m, *a[100003], e[5000010], ne, gr[100003];

void add (int i, int j)
{
	a[i][0]++;
	a[i]=(int *)realloc (a[i], (a[i][0]+1)*4);
	a[i][a[i][0]]=j;
}

void read ()
{
	ifstream fin ("ciclueuler.in");
	fin>>n>>m;
	for (int i=1;i<=n;i++)
	{
		a[i]=(int *)malloc (4);
		a[i][0]=0;
	}
	int x, y;
	for (int i=1;i<=m;i++)
	{
		fin>>x>>y;
		gr[x]++;
		gr[y]++;
		add(x, y);
		add(y, x);
	}
}

void sterge (int i, int j)
{
	int p, k;
	k=a[i][j];
	for (p=1;p<=a[k][0] && a[k][p]!=i;k++);
	a[k][p]=a[k][a[k][0]];
	a[k][0]--;		
	a[i][j]=a[i][a[i][0]];
	a[i][0]--;
}

void euler (int i)
{
	for (int j=1;j<=a[i][0];j++)
	{
		sterge (i, j);
		euler (a[i][j]);
	}
	e[++ne]=i;
}

int main ()
{
	ofstream fout ("ciclueuler.out");
	read ();
	for (int i=1;i<=n;i++)
		if (gr[i]%2==1)
		{
			fout<<"-1";
			return 0;
		}
	euler (1);
	for (int i=2;i<=m+1;i++)
		fout<<e[i]<<" ";
	return 0;
}