#include <fstream>
#include <cstdio>
#include <vector>
#define Nmax 100001
using namespace std;

ofstream g("ciclueuler.out");

int n,nr,m,ok;
bool viz[Nmax];
struct mc{
    int nod, poz;
    bool viz;
};

vector<mc> V[Nmax];
vector<int> C;

void dfs(int nod)
{
    viz[nod] = 1;
    nr++;
    for (int i=0;i<V[nod].size();i++)
        if (!viz[V[nod][i].nod])
        {
            viz[V[nod][i].nod] = 1;
            dfs(V[nod][i].nod);
        }
}
bool conex()
{
    dfs(1);
    if (nr==n)
        return 1;
    return 0;
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    scanf("%d%d",&n,&m);
    for (int i=1;i<=m;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        mc crt;
        crt.viz = 0;
        crt.nod = y;
        crt.poz = V[y].size();
        if (x==y)
            crt.poz++;
        V[x].push_back(crt);
        crt.nod = x;
        crt.poz = V[x].size()-1;
        V[y].push_back(crt);
    }

    for (int i=1;i<=n;i++)
    {
        if (V[i].size()%2==1)
        {
            g<<-1;
            return 0;
        }
    }
    if (!conex())
    {
        g<<-1;
        return 0;
    }

    C.push_back(1);

    while (!C.empty())
    {
        int nod = C.back();

        while (!V[nod].empty() && V[nod].back().viz)
            V[nod].pop_back();

        if (!V[nod].empty())
        {
            V[nod].back().viz = 1;
            V[V[nod].back().nod][V[nod].back().poz].viz = 1;
            C.push_back(V[nod].back().nod);
            V[nod].pop_back();
        }
        else
        {
            C.pop_back();
            if (!C.empty())
                g<<nod<<' ';
        }
    }


    return 0;
}