#include <fstream>
#include <vector>
#include <bitset>
using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
int n,m,i,x,y,ciclueuler=1,k,sol[500005];
bitset <500005> viz;
vector <pair<int,int>> a[100005];
void find_euler_cycle(int nod)
{
   while (!a[nod].empty())
   {
       pair<int,int> it;
       it = a[nod].back();
       a[nod].pop_back();
       if (!viz[it.second])
       {
           viz[it.second]=1;
           find_euler_cycle(it.first);
       }
   }
   sol[++k]=nod;
}
int main()
{
    in>>n>>m;
    for (i=1;i<=m;++i)
    {
        in>>x>>y;
        a[x].push_back({y,i});
        a[y].push_back({x,i});
    }
    for (i=1;i<=n;++i)
    {
        if ((a[i].size())%2)
        {
            ciclueuler=0;
            out<<"-1\n";
        }
    }
    if (ciclueuler)
        find_euler_cycle(1);
    for (i=1;i<=k-1;++i)
         out<<sol[i]<<" ";
}