#include<cstdio>
#include<vector>
#include<deque>
#include<map>

using namespace std;

int n, m;

map < pair < int , int > , bool > mp;
deque < int > vecini[100009];
vector < int > ans;

void euler (int nod)
{
    while (!vecini[nod].empty())
    {
        int vecin = vecini[nod].front();
        vecini[nod].pop_front();
        if (mp[make_pair(nod, vecin)] == 0) continue;
        mp[make_pair(nod, vecin)] = 0;
        mp[make_pair(vecin, nod)] = 0;
        euler (vecin);
    }
    ans.push_back(nod);
}

int main()
{

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

//freopen ("input", "r", stdin);
//freopen ("output", "w", stdout);

scanf ("%d %d", &n, &m);
for (int i=1; i<=m; i++)
{
    int X, Y;
    scanf ("%d %d", &X, &Y);
    vecini[X].push_back(Y);
    vecini[Y].push_back(X);
    mp[make_pair(X, Y)] = 1;
    mp[make_pair(Y, X)] = 1;
}

for (int i=1; i<=n; i++)
    if (vecini[i].size()%2 == 1)
    {
        printf ("-1\n");
        return 0;
    }

euler (1);

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