#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[500001];
bitset <500001> viz;
vector <pair<int,int>> a[100001];
void find_euler_cycle(int nod)
{
    for (i=a[nod].size()-1; i>=0; --i)
    {
        if (!viz[a[nod][i].second])
        {
            viz[a[nod][i].second]=1;
            find_euler_cycle(a[nod][i].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";
            return 0;
        }
    }
    if (ciclueuler)
        find_euler_cycle(1);
    for (i=1; i<=k-1; ++i)
        out<<sol[i]<<" ";
    out<<"\n";
    return 0;
}