# include <cstdio>
# include <vector>
# include <algorithm>
# define nmax 100001
using namespace std;
vector <int> G[nmax],sol;
int st[nmax*5], vf;
int n, m;
void dfs(int x)
{
    int y;
    st[++vf] = x;
    while(vf)
    {
        x=st[vf];
        if(G[x].size())
        {
            y=G[x].back();
            G[x].pop_back();
            st[++vf]=y;
            G[y].erase(find(G[y].begin(),G[y].end(),x));
        }
        else
        {
            vf--;
            sol.push_back(x);
        }
    }
}
bool verif()
{
    for(int i=1;i<=n;i++)
        if(G[i].size()%2) return 0;
    return 1;
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    int i,x,y;
    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);
    }
    if(verif())
    {
        dfs(1);
        for(i=0;i<sol.size()-1;i++)
            printf("%d ",sol[i]);
    }
    else printf("-1");
    return 0;
}