#include <fstream>
#include <cstdio>
#include <vector>
#include <stack>
using namespace std;


ofstream fout("ciclueuler.out");

const int NMax = 100005;
vector <int> G[NMax],Sol;
int N,M,D[NMax],Use[NMax];
stack <int> S;

const int Size = 8192;
char Buffer[Size+16];
int Pos;

inline void ReadV(int &Value)
{
    Value=0;

    while(Buffer[Pos]<'0' || Buffer[Pos]>'9')
        if(++Pos==Size) fread(Buffer, 1, Size, stdin), Pos=0;

    while(Buffer[Pos]>='0' && Buffer[Pos]<='9')
    {
        Value=Value*10+Buffer[Pos]-'0';
        if(++Pos==Size)fread(Buffer,1, Size, stdin),Pos=0;
    }
}

void Read()
{
  freopen("ciclueuler.in","r",stdin);
  //fin>>N>>M;
  ReadV(N);  ReadV(M);
  for(int i = 1; i <= M; ++i)
    {
      int x,y;
      //fin>>x>>y;
      ReadV(x);  ReadV(y);
      G[x].push_back(y);
      G[y].push_back(x);
      D[x]++;D[y]++;
    }
}

void DFS(int Nod)
{
  Use[Nod] = 1;
  for(int i = 0; i < (int)G[Nod].size(); ++i)
    {
      int Vecin = G[Nod][i];
      if(!Use[Vecin])
        DFS(Vecin);
    }
}

void Erase(int Nod, int Vecin)
{
  G[Nod].erase(G[Nod].begin());

  for(int i = 0; i < (int)G[Vecin].size(); ++i)
    if(G[Vecin][i] == Nod)
      {
        G[Vecin].erase(G[Vecin].begin()+i);
        break;
      }
}

void Cycle(int Nod)
{
    while(G[Nod].size())
    {
      int Vecin = G[Nod][0];
      Erase(Nod,Vecin);
      S.push(Nod);
      Nod = Vecin;
    }
}

void Euler()
{
  int Nod = 1;
  do
  {
    Cycle(Nod);
    Nod = S.top();S.pop();
    Sol.push_back(Nod);
  }while(!S.empty());
}

void Print()
{
  for(int i = 0; i < (int)Sol.size(); ++i)
    fout<<Sol[i]<<" ";
  fout<<"\n";
}

int main()
{
    Read();
    int Ok = 1;
    DFS(1);
    for(int i = 1; i <= N; ++i)
      if(!Use[i])
        Ok = 0;
    for(int i = 1; i <= N; ++i)
      if(D[i]%2)
        Ok = 0;

    if(!Ok)
        fout<<"-1\n";
    else
    {
      Euler();
      Print();
    }
    return 0;
}