// Graf Eulerian - O ( )
// Un graf este eulerian daca este conex si orice nod are grad par
#include <fstream>
#include <vector>
#include <bitset>
#define Nmax 100150
#define Mmax 500150
#define pb push_back
#define mp make_pair
#define x first
#define y second
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int N,M,sol[Mmax];
vector < int > G[Mmax];
vector < pair<int,int> >E;
bitset < Mmax > viz;

void ReadInput()
{
     int x,y;
     f>>N>>M;
     for(int i=0;i<M;++i)
          f>>x>>y, E.pb(mp(x,y)) , G[x].pb(i) , G[y].pb(i);
}

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 Eulerian(int N,vector < int > G[Nmax])
{
     for(int i=1;i<=N;++i)
          if(G[i].size()&1)return 0;
     return 1;
}

int main()
{
     ReadInput();
     if(Eulerian(N,G))
     {
          DFS(1);
          for(int i=1;i<=M;++i)g<<sol[i]<<' ';
          g<<'\n';
     }
     else g<<-1<<'\n';
     f.close();g.close();
     return 0;
}