#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define NMAX 100005
int n,*L[NMAX],S[NMAX],ns,nl,C[NMAX],Q[NMAX];
bool viz[NMAX];

void citire() {
	FILE *fin=fopen("ciclueuler.in","r");
	int m,i;
	fscanf(fin,"%d %d",&n,&m);
	for (i=1;i<=n;++i) {
		L[i] = (int*)realloc(L[i],sizeof(int));
		L[i][0]=0;
	}
	while (m--) {
		int x,y;
		fscanf(fin,"%d %d",&x,&y);
		++L[x][0];
		L[x]=(int*)realloc(L[x],(L[x][0]+1)*sizeof(int));
		L[x][L[x][0]]=y;
		++L[y][0];
		L[y]=(int*)realloc(L[y],(L[y][0]+1)*sizeof(int));
		L[y][L[y][0]]=x;
	}
	fclose(fin);
}

int eulerian() {
	int i;
	for (i=1;i<=n;++i)
		if (L[i][0]%2) return 0; 
	return 1;
}

void sterge(int v, int w) {
	int poz=0,i;
	for (i=1;i<=L[v][0]&&!poz;++i)
		if (L[v][i]==w) poz=i;
	for (i=poz;i<L[v][0];++i)
	L[v][i]=L[v][i+1];
	L[v][0]--;
	poz=0;
	for (i=1;i<=L[w][0]&&!poz;++i)
		if (L[w][i]==v) poz=i;
	for (i=poz;i<L[w][0];++i)
		L[w][i]=L[w][i+1];
	L[w][0]--;
}

void euler(int v) {
	while (L[v][0]) {
		int w=L[v][1];
	S[++ns]=v;
	sterge(v,w);
	v=w;
	}
}

int ver() {
	int v=eulerian();
	if (!v) return 0;
	ns=nl=0;

	do {
		euler(v);
		v=S[ns--];
		C[++nl]=v;
	} while (ns);
	return 1;
}

void afisare(int sol) {
	FILE *fout=fopen("ciclueuler.out","w");
	if (!sol)
		fprintf(fout,"-1\n");
	else {
		int i;
		fprintf(stderr,"%d\n",nl);
		for (i=nl;i;--i)
		fprintf(fout,"%d ",C[i]);
	}
	fclose(fout);
}

int main() {
	citire();
	afisare(ver());
	return 0;
}