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

using namespace std;
FILE *f,*g;

struct name
{
    int ve,mu;
};
vector <name> v[100002];
bool viz[500002];
deque <int> q;

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