#include <cstdio>
        #include <vector>
        #include <list>
        using namespace std;
        vector <int> g[100001];
        vector <int> sol;
        vector <int> :: iterator it;
        list <int> q;
        void euler (void)
        {
            int nod, y; q.push_back(1);
            while (!q.empty())
            {
                nod=q.back();
                if (!g[nod].empty())
                {
                    y=g[nod].back();
                    q.push_back(y);
                    g[nod].pop_back();
                    for (it=g[y].begin(); it!=g[y].end(); it++)
                    {
                        if (*it==nod)
                        {
                            g[y].erase(it);
                            break;
                        }
                    }
                }
                else
                {
                    sol.push_back(nod);
                    q.pop_back();
                }
            }
        }
        int main()
        {
            int n, m, i, x, y;
            freopen("ciclueuler.in","r",stdin);
            freopen("ciclueuler.out","w",stdout);
            scanf("%d%d",&n,&m);
            for (i=1; i<=m; i++)
            {
                scanf("%d%d",&x,&y);
                g[x].push_back(y);
                g[y].push_back(x);
            }
            for (i=1; i<=n; i++)
            {
                if (g[i].size()%2==1)
                {
                    printf("-1");
                    return 0;
                }
            }
            euler();
            for (i=0; i<sol.size(); i++)
            {
                printf("%d ",sol[i]);
            }
            return 0;
        }