#include <stdio.h>
#define MaxN 100001
int n, m;
struct nod {
	int inf, edge,elim;
	nod *urm,*ant;
};
nod *L[MaxN];
bool viz[MaxN];
int grad[MaxN];
void add(int ex1, int ex2){
	nod *p, *q;
	p = new nod;
	p->inf = ex2;
	p->urm = L[ex1];
	p->ant = NULL;
	p->edge = 0;
	p->elim = 0;
	if (p->urm != NULL) p->urm->ant = p;
	L[ex1] = p;
	q = new nod;
	q->inf = ex1;
	q->urm = L[ex2];
	q->ant = NULL;
	q->edge = 0;
	q->elim = 0;
	if (q->urm != NULL) q->urm->ant = q;
	L[ex2] = q;
};

void DFS(int x){
	viz[x] = true;
	printf("%d ",x);
	nod *q;
	for (nod *p = L[x]; p != NULL; p = p->urm)
		if (!viz[p->inf]){
			p->edge = 1;
			for (q = L[p->inf]; q != NULL && q->inf != x; q = q->urm);
			if (q !=NULL && q->inf == x) q->edge = 1;

			DFS(p->inf);
		};
};

void Euler(){
	int ex1,ex2,much;
	ex1 = 1;
	nod *p = L[1];
	nod *q;
	printf("%d ",ex1);
	much = 1;
	while (much < m){
			for (q = p; q != NULL && (q->edge == 1 || q->elim == 1); q = q->urm);
			if (q == NULL){
				for (q = p; q != NULL && (q->elim == 1); q = q->urm);
				 p = q;
			}; //daca nu avem decat bridge-uri
				ex2 = q->inf;
				q->elim = 1;
			//if (ex2 != 1)
				printf("%d ",ex2);
				much ++;
			for (q = L[ex2]; q != NULL && (q->inf != ex1); q = q->urm);
			q->elim = 1;
/*
			if (q->ant != NULL){					 //in caz in care nu este primul nod din lista
				q -> ant ->urm = q->urm;
			} else {								 //daca este primul nod din lista
				L[ex1] = L[ex1]->urm;
			};
			if (q->urm != NULL)						 //daca nu este ultimul nod din lista
				q -> urm ->ant = q->ant;
			delete q;								 //eliminam memoria alocata muchiei eliminate
			
			

			if (q->ant != NULL){					 //in caz in care nu este primul nod din lista
				q -> ant ->urm = q->urm;
			} else {				   				//daca este primul nod din lista
				L[ex2] = L[ex2]->urm;
			};
			if (q->urm != NULL)		 				//daca nu este ultimul nod din lista
				q -> urm ->ant = q->ant;
			delete q;
			*/
			p = L[ex2];								//trecem la cealalta extremitate
			ex1 = ex2;				
			}
};


int main(){
	int ex1, ex2;
	freopen("ciclueuler.in","r",stdin);
	freopen("ciclueuler.out","w",stdout);
	scanf("%d %d",&n, &m);
	for (int i = 1; i <= m; i++){
		scanf("%d %d", &ex1, &ex2);
		add(ex1,ex2);
		grad[ex1]++;
		grad[ex2]++;
	};
	DFS(1);
	for (int i = 1; i <= n; i++){
		if (grad[i] % 2) {
			printf("-1");
			return 0;
		};
		if (viz[ i ] != true )  {
			printf("-1");
			return 0;
		};
	};
	printf("\n");
	Euler();
};