#include<cstdio>
#include<algorithm>
#include<vector>
#include<cstring>
#include<deque>
using namespace std;
int n,i,j,nr,m,x,y;
vector < int > V[100005];
deque < int > q;
int w[100005];
void citire()
{
    int i;
    scanf("%d %d",&n,&m);
    for (i=1;i<=m;++i)
    {
        scanf("%d %d",&x,&y);
        V[x].push_back(y);
        V[y].push_back(x);
    }
}
void df(int x)
{
    w[x]=1;
    int i;
    for (i=0;i<V[x].size();i++)
    if (!w[V[x][i]])
    df(V[x][i]);
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    citire();
    df(1);
    for (i=1;i<=n;i++)
    if ((V[i].size()%2==1)||(!w[i]))
    {
        printf("-1\n");
        return 0;
    }
    q.push_front(1);
    while (!q.empty())
    {
        x=q.front();
        if (V[x].size()==0)
        {q.pop_front(); printf("%d ",x);}
        else
        {
            y=V[x].back();
            q.push_front(y);
            V[y].erase(find(V[y].begin(),V[y].end(),x));
            V[x].pop_back();
        }
    }
    return 0;
}