#include<cstdio>
struct Nod
{int info;
Nod *urm;};
int a[500005],b[500005],d[500005],i,n,m,k,w[100001],*g[100001],j,c[100001],t;
Nod *l,*r;

void I(Nod *&l)
{int e,i,k,t,j;
Nod *p=l,*r,*q=l->urm;
do
       {for(k=-1,i=0;i<w[p->info]&&k==-1;i++)
               j=g[p->info][i],k=i;
       for(e=k;e<w[p->info]-1;e++)
               g[p->info][e]=g[p->info][e+1];
       w[p->info]--;
       for(k=-1,t=0;t<w[j]&&k==-1;t++)
       if(g[j][t]==p->info)
               k=t;
       for(e=k;e<w[j]-1;e++)
               g[j][e]=g[j][e+1];
       w[j]--;
       r=new Nod;
       r->info=j,r->urm=NULL,p->urm=r,p=r;}
while(r->info!=l->info);
p->urm=q;}

int A(Nod *&l)
{Nod *p=l;
while(p)
       {if(w[p->info]>0)
             {I(p);
             return 1;}
       p=p->urm;}
return 0;}

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

void D(int k)
{int i,sp=1,st[100001];
st[1]=k,c[k]=1;
while(sp)
      {j=st[sp--];
      for(i=0;i<w[j];i++)
      if(!c[g[j][i]])
             c[g[j][i]]=1,st[++sp]=g[j][i];}}

int O()
{D(1);
for(int i=1;i<=n;i++)
if(!c[i])
      return 0;
return 1;}

int main()
{freopen("ciclueuler.in","r",stdin);
freopen("ciclueuler.out","w",stdout);
scanf("%d%d",&n,&m);
for(i=1;i<=m;i++)
      scanf("%d%d",&a[i],&b[i]),w[a[i]]++,w[b[i]]++;
for(i=1;i<=n;w[i++]=0)
      g[i]=new int[w[i]];
for(i=1;i<=m;i++)
      g[a[i]][w[a[i]]++]=b[i],g[b[i]][w[b[i]]++]=a[i];
if(!O()||!P())
      printf("-1");
else
      {l=new Nod;
      l->info=1,l->urm=NULL;
      while(A(l));
      for(r=l->urm;r;r=r->urm)
             printf("%d ",r->info);}
return 0;}