#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define Nmax 100002
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
vector <int> G[Nmax],sol;
stack <int> S;
int n,use[Nmax];
void read()
{int m;
    fin>>n>>m;
    int i;
    for(i=1;i<=m;i++)
    {
        int x,y;
        fin>>x>>y;
        G[x].push_back(y);
        G[y].push_back(x);

    }
}
void Erase(int nod1, int nod2)
{
    G[nod1].erase(G[nod1].begin());

    for(unsigned int i=0;i<G[nod2].size();i++)
        if(G[nod2][i]==nod1)
        {
            G[nod2].erase(G[nod2].begin()+i);
            break;
        }
}

void cycle(int nod)
{
    while(G[nod].size())
    {
        S.push(nod);
        int vecin=G[nod][0];
        Erase(nod,vecin);
        nod = vecin;
    }
}

void solve()
{
 int nod=1;
     do
    {
        cycle(nod);
        nod=S.top();
        S.pop();
        sol.push_back(nod);
    }
    while(!S.empty());
}
void DFS(int x)
{
    use[x]=1;
    for(unsigned int i=0;i<G[x].size();i++)
        if(!use[G[x][i]])
        DFS(G[x][i]);
}
int verif_euler()
{
    DFS(1);
    for(int i=1;i<=n;i++)
    {
         if(use[i]==0) return 0;
         if(G[i].size()%2!=0) return 0;
    }



    return 1;
}


int main()
{
    read();
    if(verif_euler()==0) fout<<"-1";
    else
    {
        solve();
     for(unsigned int i=0;i<sol.size();i++)
        fout<<sol[i]<<" ";
    }

    return 0;
}