# include <cstdio>
# include <vector>
# include <stack>
using namespace std;

FILE *f = freopen("ciclueuler.in", "r", stdin);
FILE *g = freopen("ciclueuler.out", "w", stdout);

const int N_MAX = 500001;

struct muchie{
    int index;
    int capat;

    muchie (int a, int b)
    {
        this->index = a;
        this->capat = b;
    }
};

vector <muchie> G[N_MAX];
vector <int> sol;
stack <int> stiva;
int grad[N_MAX], n, M, m;
bool viz[N_MAX];
bool OK = true;

void add_edge(int x, int y)
{
    grad[x] ++;
    grad[y] ++;

    M++;

    G[x].push_back(muchie(M, y));
    G[y].push_back(muchie(M, x));
}

int delete_neighbour(int nod)
{
    while (!G[nod].empty() && viz[G[nod].back().index])
        G[nod].pop_back();

    if (!G[nod].empty())
    {
        muchie muc = G[nod].back();

        viz[muc.index] = true;

        grad[nod] --;
        grad[muc.capat] --;

        G[nod].pop_back();
        M--;

        return muc.capat;
    }

    return 0;
}

void solve()
{
    int start;

    for (start = 1; grad[start] == 0; start ++);

    stiva.push(start);

    while (!stiva.empty())
    {
        int nod = stiva.top();

        if (grad[nod])
            stiva.push(delete_neighbour(nod));
        else
        {
            sol.push_back(nod);
            stiva.pop();
        }
    }
}

void read()
{
    scanf("%d %d", &n, &m);

    for (int i=1; i<=m; i++)
    {
        int x, y;
        scanf("%d %d", &x, &y);

        add_edge(x, y);
    }

    for (int i=1; i<=n; i++)
    {
        if (grad[i] % 2 == 1)
        {
            OK = false;
            return ;
        }
    }
}

int main()
{
    read();
    if (OK)
        solve();

    if (M != 0)
        OK = false;

    if (!OK)
        printf("-1\n");
    else
    {
        //printf("%d\n", sol.size());

        for (int i=0; i<sol.size() - 1; i++)
            printf("%d ", sol[i]);
    }

    return 0;
}