#include <cstdio>
#include <stack>
#include <vector>
#include <queue>

using namespace std;
#define MAXM 500005
#define MAXN 100005


struct muchie
{
    int a, b;
    bool ex;
};
vector<int> v[MAXN], sol;
stack<int> st;
muchie muc[MAXM];
int n, m, vec[MAXN];
bool viz[MAXN];
void eul(int sursa);
bool isEul();

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    int i, a, b;
    scanf("%d%d", &n, &m);
    for(i=1; i<=m; i++)
    {
        scanf("%d%d", &a, &b);
        v[a].push_back(i);
        v[b].push_back(i);
        muc[i].a = a; muc[i].b = b; muc[i].ex = 1;
        vec[a]++; vec[b]++;
    }
    if(!isEul())
    {
        printf("-1");
        return 0;
    }
    eul(1);
    vector<int>::iterator it;
    for(int i=0; i<=sol.size()-2; i++)
        printf("%d ", sol[i]);
    return 0;
}
void eul(int sursa)
{
    int tata, fiu;
    vector<int>::iterator it;
    st.push(sursa);
    while(!st.empty())
    {
        tata = st.top();
        while(v[tata].size())
        {
            if(muc[v[tata].back()].ex)
                break;
            v[tata].pop_back();
        }
        if(v[tata].empty())
        {
            sol.push_back(tata);
            st.pop();
        }
        else{
            int n1 = muc[v[tata].back()].a;
            int n2 = muc[v[tata].back()].b;
            if(tata == n1)
                fiu = n2;
            else
                fiu = n1;
            st.push(fiu);
            muc[v[tata].back()].ex = 0;
            v[tata].pop_back();
        }
    }
}
void bfs(int nod)
{
    int tata;
    queue<int> q;
    vector<int>::iterator it;
    q.push(nod);
    while(!q.empty())
    {
        tata = q.front();
        q.pop();
        for(it=v[tata].begin(); it!=v[tata].end(); ++it)
            if(!viz[*it])
            {
                viz[*it] = 1;
                q.push(*it);
            }
    }
}
bool isEul()
{
    int i, fiu;
    vector<int>::iterator it;
    for(i=1; i<=n; i++)
        if(v[i].size() % 2)
            return 0;
    bfs(1);
    for(i=2; i<=n; i++)
        if(!viz[i])
            return 0;
    return 1;
}