# include <cstdio>
# include <vector>
# define pb push_back
# define N 100010
# define M 500010

using namespace std;

vector <int> G[N];
vector <int> st;
vector <int> :: iterator it;

int n,m;


void load()
{
    int x,y;
    scanf("%d %d\n", &n, &m);
    while(m--)
    {
        scanf("%d %d\n", &x, &y);
        G[x].pb(y);
        G[y].pb(x);
    }
}

bool verif()
{
    int i;
    for(i=1; i<=n; ++i)
        if((G[i].size())%2!=0) return false;
    return true;
}

vector <int> :: iterator find(int x, int nod)
{
    vector <int> :: iterator it;
    for(it=G[nod].begin(); it!=G[nod].end(); ++it)
        if((*it)==x) return it;
}

void euler(int x)
{
    int i,nod;
    if(G[x].empty())
    {
        printf("%d ", x);
        st.pop_back();
    }
    for(vector <int> :: iterator it=G[x].begin(); it!=G[x].end() && !G[x].empty(); ++it)
    {
        nod=(*it);
        G[x].erase(it);
        G[nod].erase(find(x, nod));
        st.pb(nod);
        euler(nod);
    }
}

void write()
{
    int i;
    for(i=st.size()-1; i>=0; --i)
        printf("%d ", st[i]);
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    load();
    if(verif()) euler(1);
    else printf("-1\n");

    write();

    fclose(stdin);
    fclose(stdout);
    return 0;
}