#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <bitset>

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

vector <pair <int,int> > G[100005];
stack <int> S;
bitset <500005> B;
int n,m;
void citire()
{
    fin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x,y;
        fin>>x>>y;
        G[x].push_back({i,y});
        G[y].push_back({i,x});
    }
}
void euler()
{
    S.push(1);
    while(!S.empty())
    {
        int x=S.top();
        int ok=0;///inca n-am facut ciclu;
        while(G[x].size()&&B[G[x].back().first]) ///daca elementul luat de la coada listei de vecini are muchia parcursa , o eliminam
            G[x].pop_back();
        if(!G[x].empty())
        {
           int vecin=G[x].back().second;
           B[G[x].back().first]=1;///folosim muchia in ciclu;
           ok=1;///am ggasit cu ce sa continuam
           G[x].pop_back();///eliminam muchia
           S.push(vecin); ///punem  elementul in ciclu
        }
        if(!ok)///daca n am continuat afisam si ne intoarcem
        {
            S.pop();
            if(!S.empty()) fout<<S.top()<<" ";
        }
    }
}
void rezolva()
{
    int ok=0;
    for(int i=1; i<=n; i++)
    if(G[i].size()%2) {ok=1; fout<<"-1";}
    if(!ok)
        euler();
}
int main()
{
    citire();
    rezolva();
    return 0;
}