#include <fstream>

using namespace std;

ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");

#define N 100001
#define M 500001

int n, m;
int lst[N], vf[2 * M], urm[2 * M], mch[2 * M], nvf = 0;
int stiva[2 * M], st = 0;
int cicluEulerian[2 * M], nce = 0;
bool ok[M];

int main()
{
    in >> n >> m;

    for(int i = 1; i <= m; i++)
    {
        int x, y;
        in >> x >> y;
        vf[++nvf] = y;
        urm[nvf] = lst[x];
        mch[nvf] = i;
        lst[x] = nvf;
        vf[++nvf] = x;
        urm[nvf] = lst[y];
        mch[nvf] = i;
        lst[y] = nvf;
    }

    stiva[++st] = 1;
    while(st)
    {
        int x = stiva[st];
        bool blocat = 1;
        for(int i = lst[x]; i; i = urm[i])
            if(!ok[mch[i]])
            {
                stiva[++st] = vf[i];
                ok[mch[i]] = 1;
                blocat = 0;
                break;
            }
        if(blocat)
        {
            st--;
            cicluEulerian[++nce] = x;
        }
    }

    for(int i = 1; i <= nvf; i++)
        if(!ok[mch[i]])
        {
            out << "-1\n";
            return 0;
        }

    if(cicluEulerian[1] != cicluEulerian[nce])
    {
        out << "-1\n";
        return 0;
    }

    for(int i = 1; i < nce; i++)
        out << cicluEulerian[i] << ' ';
    out << '\n';
}