#include <cstdio>
#include <cstring>
#include <vector>
#include <deque>
#include <algorithm>
#define mp make_pair
#define f first
#define s second
#define maxN 100002
using namespace std;
int n, i, j, m, ok, x, y;
deque < int > q;
vector < pair < int, int> > V[maxN];
bool used[maxN * 5];
void read()
{
    freopen("ciclueuler.in", "r", stdin);
    scanf("%d %d", &n, &m);
    i = 0;
    while (m --)
    {
        ++ i;
        scanf("%d %d", &x, &y);
        V[x].push_back(mp(y, i));
        V[y].push_back(mp(x, i));
    }
}
void solve()
{
    ok = 1;
    for (i = 1;i <= n;++ i)
    if (V[i].size() % 2)
    {
        ok = 0;
        return ;
    }
}
void write()
{
    freopen("ciclueuler.out", "w", stdout);
    if (!ok)
    {
        printf("-1");
        return ;
    }
    q.push_back(1);
    while (!q.empty())
    {
        x = q.front();
        while (!V[x].empty() && used[V[x].back().s])
            V[x].pop_back();
        if (V[x].size() == 0)
        {
            q.pop_front();
            printf("%d ", x);
        }
        else
        {
            y = V[x].back().f;
            used[V[x].back().s] = 1;
            V[x].pop_back();
            q.push_front(y);
        }
    }
}
int main()
{
    read();
    solve();
    write();
    return 0;
}