#include<fstream>
#include<vector>
#include<bitset>
#include<deque>
#include<algorithm>
using namespace std;
vector <int> L[100002];
bitset <100002> u;
deque <int> q;
int n, m, x, y, i, ok, nod, next;
void dfs(int nod)
{
    for(int i=0; i<L[nod].size(); i++)
    {
        int fiu=L[nod][i];
        if(u[fiu]==0)
        {
            u[fiu]=1;
            dfs(fiu);
        }

    }
}
void euler(int nod)
{
    while(!L[nod].empty())
    {
        q.push_back(nod);
        next=L[nod].back();
        L[nod].pop_back();
        L[next].erase(find(L[next].begin(), L[next].end(), nod));
        nod=next;
    }
}
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
int main()
{
    in>>n>>m;
    for(i=1; i<=m; i++)
    {
        in>>x>>y;
        L[x].push_back(y);
        L[y].push_back(x);
    }
    u[1]=1;
    dfs(1);
    ok=1;
    for(i=1; i<=n; i++)
    {
        if(u[i]==0 || L[i].size()&1!=0)
        {
            ok=0;
            break;
        }
    }
    if(!ok)
        out<<"-1";
    else
    {
        nod=1;
        do
        {
            euler(nod);
            nod=q.back();
            q.pop_back();
            out<<nod<<" ";
        }
        while(!q.empty());
    }
    return 0;
}