#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
const int maxn=100005;
const int maxm=500005;
vector <int> G[maxn];
bool Mviz[maxm];
int N,M,from[maxn],to[maxn];
int main()
{
    int i,x,y,nod;
    f>>N>>M;
    for (i=0;i<M;i++)
    {
        f>>x>>y;
        G[x].push_back(i);
        G[y].push_back(i);
        from[i]=x;
        to[i]=y;
    }
    for (i=1;i<=N;i++)
        if (G[i].size()%2!=0) {g<<"-1";return 0;}

    vector <int> ans;
    vector <int> stk;
  //  stk.push(1);
    stk.push_back(1);
    while(!stk.empty())
    {
        nod=stk.back();
        if (G[nod].empty()==0)
        {
            int e=G[nod].back();
            G[nod].pop_back();
            if (Mviz[e]==0)
            {
                Mviz[e]=1;
                int next=from[e];
                if (next==nod) next=to[e];
                stk.push_back(next);
            }
        }
        else
        {
            stk.pop_back();
            ans.push_back(nod);
        }
    }
     for (i=0;i<ans.size()-1;i++)
        g<<ans[i]<<' ';
}