#include <stdio.h>

using namespace std;
FILE*f=fopen("ciclueuler.in","r");
FILE*g=fopen("ciclueuler.out","w");
int k,gr[100500],sol[100500],n,m;
int st[100500];
struct nod{
int inf;
nod *urm;

} *l[100500];
void adaug(nod *&p,int x){
nod *u;
u=new nod;
u->inf=x;
u->urm=p;
p=u;


}
void sterg(nod *&p,int x){
nod *aux,*u;
u=p;
if(u->inf==x) {p=p->urm; delete u;return;}
while(u->urm&&u->urm->inf!=x) u=u->urm;
    if(u->urm){
        aux=u->urm;
        u->urm=u->urm->urm;
        delete aux;

    }

}



int main()
{
fscanf(f,"%d%d",&n,&m);
int i,x,y;
for(i=1;i<=m;i++){
  fscanf(f,"%d%d",&x,&y);
adaug(l[x],y);
adaug(l[y],x);
gr[x]++;
gr[y]++;
}
for(i=1;i<=n;i++) {if(gr[i]%2==1) {
    fprintf(g,"-1\n");

 return 0;}
int poz=0;
st[++poz]=1;
while(poz){
    int x=st[poz];
    if(l[x]){
            int w=l[x]->inf;
        st[++poz]=w;
        sterg(l[w],x);
        sterg(l[x],w);

    }
    else sol[++k]=st[poz--];


}
}
for(i=1;i<=m;i++) fprintf(g,"%d ",sol[i]);
    return 0;
}