#include <fstream>
#include <vector>
#define NMAX 100002
#define MMAX 500002

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int n,m;
struct varf{int x,nr;};
vector<varf> G[MMAX];
vector<int> C;

bool sters[MMAX];

void euler(int x)
{
    varf aux;
    while(!G[x].empty())
        {
         aux=G[x].back();
         G[x].pop_back();
         if(!sters[aux.nr])
            {
             sters[aux.nr]=1;
             euler(aux.x);
            }
        }
    C.push_back(x);
}

int main()
{
    int i,x,y;
    fin>>n>>m;
    for(i=1; i<=m; i++)
        {
         fin>>x>>y;
         G[x].push_back({y,i});
         G[y].push_back({x,i});
        }
    //verificare toate gradele pare
    for(i=1; i<=n; i++)
        if(G[i].size()%2==1)
            {
             fout<<-1<<'\n';
             return 0;
            }
    //gasesc primul nod care are grad diferit de 0
    for(i=1; i<=n; i++)
        if(G[i].size())
            {
             euler(i);
             break;
            }
    if(C.size()!=m+1)
        {
         fout<<-1<<'\n';
         return 0;
        }
    for(i=0; i<C.size()-1; i++)
        fout<<C[i]<<' ';
    return 0;
}