#include <fstream>
#include <cstdio>
#include <set>
#include <stack>
#include <vector>
#include <string>
#include <algorithm>
#define DIM 100001
using namespace std;
FILE *fi;
ofstream fo("ciclueuler.out");
int n,m;
vector<int> V[DIM],REZ;
pair<int,int> M[5*DIM];
bool VIZ[5*DIM],ok=true;
stack<int> S;
char buff[DIM];
int poz=0;
string afis;
void citeste(int &numar)
{
     numar = 0;
     //cat timp caracterul din buffer nu e cifra ignor
     while (buff[poz] < '0' || buff[poz] > '9')
          //daca am "golit" bufferul atunci il umplu
          if (++poz == DIM)
               fread(buff,1,DIM,fi),poz=0;
     //cat timp dau de o cifra recalculez numarul
     while ('0'<=buff[poz] && buff[poz]<='9')
     {
          numar = numar*10 + buff[poz] - '0';
          if (++poz == DIM)
               fread(buff,1,DIM,fi),poz=0;
     }
}
void scrie(int x)
{
    string s="";
    while(x)
    {
        s+=(char)(x%10+'0');
        x/=10;
    }
    reverse(s.begin(),s.end());
    afis+=s;
    afis+=" ";
}
int main()
{
    fi=fopen("ciclueuler.in","r");
    citeste(n);
    citeste(m);
    for(int i=1;i<=m;i++)
    {
        int a,b;
        citeste(a);
        citeste(b);
        V[a].push_back(i);
        V[b].push_back(i);
        M[i]=make_pair(a,b);
    }
    for(int i=1;i<=n;i++)
        if(V[i].size()==0 || V[i].size()%2==1)
            ok=false;
    if(!ok)
        fo<<-1;
    else
    {
        S.push(1);
        while(!S.empty())
        {
            int v=S.top();
            int i=0;
            while(i<V[v].size()&&VIZ[V[v][i]])
                i++;
            if(i==V[v].size())
            {
                S.pop();
                scrie(v);
            }
            else
            {
                int to=M[V[v][i]].first;
                if(to==v && M[V[v][i]].first!=M[V[v][i]].second)
                    to=M[V[v][i]].second;
                VIZ[V[v][i]]=true;
                S.push(to);
            }
        }
        fo<<afis;
    }
    fo.close();
    return 0;
}