#include <cstdio>
#include <vector>
#include <deque>

using namespace std;
FILE *f,*g;

struct name
{
    int a,b;
};
vector <name> nod[100002];
bool viz[1000002];
int nr=0,n;
deque <int> coada;
void euler(int no)
{
    int vecin,muchie;
    while(!nod[no].size())
    {
        vecin=nod[no].back().a;
        muchie=nod[no].back().b;
        nod[no].pop_back();
        if(!viz[muchie])
            viz[muchie]=1,euler(vecin);
    }
    coada.push_back(no);

}
int main()
{
    f=fopen("ciclueuler.in","r");
    g=fopen("ciclueuler.out","w");
    int m,x,y;
    fscanf(f,"%d %d",&n,&m);
    for(int i=1;i<=m;++i)
    {
        fscanf(f,"%d %d",&x,&y);
        nod[x].push_back({y,i});
        nod[y].push_back({x,i});
    }
    for(int i=1;i<=n;++i)
        if(nod[i].size()%2!=0)
        {
            fprintf(g,"-1");
            return 0;
        }
    euler(1);
    coada.pop_back();
    while(!coada.empty())
    {
        x=coada.front();
        coada.pop_front();
        fprintf(g,"%d ",x);
    }
    fclose(f);
    fclose(g);
    return 0;
}