#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
int j,l,v1,x,y,i,n,m,val,u,nr;
vector < int > v;
vector < int > h[100002];
vector < int >::iterator it;
char a[40];
int main(){
  freopen("ciclueuler.in","r",stdin);
  freopen("ciclueuler.out","w",stdout);
   scanf("%d",&n); scanf("%d\n",&m);
  for(i=1;i<=m;i++){
    gets(a);
     l=strlen(a)-1;
    x=0;
    for(j=0;a[j]!=' ';j++) x=x*10+a[j]-48;
    y=0;
    for(j=j+1;j<=l;j++)y=y*10+a[j]-48;
  h[x].push_back(y);
  h[y].push_back(x);
 }
for(i=1;i<=n;i++)
 if(h[i].size()%2==1){
     printf("-1\n");
      return 0;
    }
 u=1;
  v.push_back(1);
   nr=0;
 while(u>0){
   if(nr==m) return 0;
    if(h[v[u-1]].size()==0){
     printf("%d ",v[u-1]);
      u--;
     v.erase(v.begin()+u);
  }
  else{
     v1=v[u-1];
     val=h[v1][0];
     h[v1].erase(h[v1].begin());
    for(it=h[val].begin();it!=h[val].end();it++)
      if(*it==v1){
        h[val].erase(it);
          break;
         }
      u++;
     v.push_back(val);
      }
   }
return 0;
}