#include <cstdio>
#include <bitset>
#include <algorithm>
#include <vector>
#define Nmax 100099
#define Mmax 500099
using namespace std;

int N,M,sol[Mmax];
bitset < Mmax > viz;

struct edge {int x,y;} E[Mmax];
vector < int > G[Nmax];

inline void DFS(int node)
{
     for(vector < int >::iterator it=G[node].begin();it!=G[node].end();++it)
          if(!viz[*it])
          {
               viz[*it]=1;
               DFS(E[*it].x+E[*it].y-node);
          }
     sol[++sol[0]]=node;
}

inline bool isEuler()
{
     for(int i=1;i<=N;++i)
          if(G[i].size() % 2==1)return 0;
     return 1;
}

int main()
{
     freopen("ciclueuler.in","r",stdin);
     freopen("ciclueuler.out","w",stdout);
     scanf("%d %d",&N,&M);
     for(int i=1;i<=M;++i)
     {
          int  x,y;
          scanf("%d %d",&x,&y);
          G[x].push_back(i) ,G[y].push_back(i);
          E[i].x=x,E[i].y=y;
     }

     if(isEuler())
     {
          DFS(1);
          for(int i=1;i<=sol[0];++i)
               printf("%d ",sol[i]);
          printf("\n");
     }
     else printf("-1\n");
     return 0;
}