#include <iostream>
#include <fstream>
#define DIM 100001
#include <vector>

using namespace std;

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

int n,m,x,y,i,j,elim[5*DIM];
struct muchie
{
    int ex;
    int ind;
};
vector<muchie>L[DIM];
bool ok;
int sol[5*DIM],k;
void ciclu(int x)
{
    while(!L[x].empty())
    {
        int nod=L[x].back().ex;
        int mch=L[x].back().ind;
        L[x].pop_back();
        if(elim[mch]==0)
        {
            elim[mch]=1;
            ciclu(nod);
        }
    }
    sol[++k]=x;
}
int main()
{
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        L[x].push_back({y,i});
        L[y].push_back({x,i});
    }
    for(i=1;i<=n;i++)
        if(L[i].size()%2!=0)
        {
            fout<<-1;
            return 0;
        }
    ciclu(1);
    for(i=1;i<k;i++)
        fout<<sol[i]<<" ";
    return 0;
}