#include <cstdio>
#include <vector>
#include <stack>
using namespace std;
#define nmax 100010
#define mmax 500010
#define f first
#define s second

vector <int> g[nmax];
stack <int> s;
int n, m, sol[mmax], l, p[nmax], x[mmax], y[mmax];
char u[mmax];

void df()
{
	int nod, v, i, prec=0, ok;
	s.push(1);
	while (!s.empty())
	{
		nod=s.top();
		ok=0;
		for (i=p[nod]; i<g[nod].size(); i++)
			if (!u[g[nod][i]])
			{
				u[g[nod][i]]=1;
				if (nod == x[g[nod][i]]) s.push(y[g[nod][i]]); else
					s.push(x[g[nod][i]]);
				p[nod]=i+1;
				ok=1;
				break;
			}
		if (!ok)
		{
			sol[++l] =  s.top();
			s.pop();
		}
	}
}

int main()
{
	freopen("ciclueuler.in","r",stdin);
	freopen("ciclueuler.out","w",stdout);
	scanf("%d %d", &n, &m);
	int i;
	for (i=1; i<=m; i++)
	{
		scanf("%d %d", &x[i], &y[i]);
		g[x[i]].push_back(i);
		g[y[i]].push_back(i);
	}
	for (i=1; i<=n; i++)
		if (g[i].size() & 1)
		{
			printf("-1\n");
			return 0;
		}
	df();
	for (i=1; i<=l; i++) printf("%d ",sol[i]);
	printf("\n");
	return 0;
}