//#include <fstream>
#include <cstdio>
#include <vector>
using namespace std;

//ifstream f("ciclueuler.in");
//ofstream g("ciclueuler.out");

int n, m, x[500001], y[500001], sol[500001];
bool mc[500001];
vector <int> A[100001];

inline void Euler(int nod)
{	for (int i=0; i<A[nod].size(); i++)
    {
        if (!mc[A[nod][i]])
        {
            mc[A[nod][i]] = true;
            Euler(x[A[nod][i]] + y[A[nod][i]] - nod);
        }
    }
    sol[++sol[0]] = nod;
}

int main()
{	freopen("ciclueuler.in","r",stdin);
	freopen("ciclueuler.out","w",stdout);
    scanf("%d%d",&n,&m);//f >> n >> m;
    for (int i = 1; i <= m; ++i)
    {   scanf("%d%d",&x[i],&y[i]);  //f >> x[i] >> y[i];
        A[x[i]].push_back(i);
        A[y[i]].push_back(i);
    }

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

    Euler(1);
    for (int i = 1; i <= sol[0]; ++i)
       printf("%d ",sol[i]); //g << sol[i] << ' ';
	printf("\n"); //g << '\n';
    //g.close();
    return 0;
}