#include <stdio.h>
long a[4][1000001],st[100001],fin[100001],i,x,y,n,m,k,l,stiva[100001],poz[100001];
void dfs()
{stiva[1]=1;l=1;poz[1]=st[1];
 while(l)
  {i=poz[l];
   while(i!=0)
    {if(a[3][i]==0)
     {a[3][i]=1;if(i%2)a[3][i+1]=1;else a[3][i-1]=1;
      l++;stiva[l]=a[1][i];poz[l-1]=i;poz[l]=st[a[1][i]];
      i=st[a[1][i]];
     }
     else i=a[2][i];
    }
   l--;
   k++;if(k<=m)printf("%ld ",stiva[l]);
  }
}
int main()
{freopen("ciclueuler.in","r",stdin);freopen("ciclueuler.out","w",stdout);
 scanf("%ld%ld",&n,&m);
 for(i=1;i<=m;i++)
  {scanf("%ld%ld",&x,&y);
   if(fin[x]==0){st[x]=fin[x]=l+1;l++;a[1][l]=y;}
	  else{a[2][fin[x]]=l+1;fin[x]=l+1;l++;a[1][l]=y;}
   if(fin[y]==0){st[y]=fin[y]=l+1;l++;a[1][l]=x;}
	  else{a[2][fin[y]]=l+1;fin[y]=l+1;l++;a[1][l]=x;}

  }
 dfs();
 fclose(stdin);fclose(stdout);
 if(k<m){freopen("ciclueuler.out","w",stdout);printf("-1");fclose(stdout);}
 return 0;
}