#include <iostream>
#include <fstream>
#define DIM 100001
#include <vector>

using namespace std;

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

int n,m,x,y,i,j,elim[5*DIM];
struct muchie
{
    int ex;
    int ind;
};
vector<muchie>L[DIM];
int s[5*DIM],vf;
bool ok;
int ciclu[5*DIM],k;
int main()
{
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        L[x].push_back({y,i});
        L[y].push_back({x,i});
    }
    for(i=1;i<=n;i++)
        if(L[i].size()%2!=0)
        {
            fout<<-1;
            return 0;
        }
    vf=1;
    s[1]=1;
    int k=0;
    while(vf)
    {
        ok=0;
        int crt=s[vf];
        while(!L[crt].empty()){
            int nod=L[crt].back().ex;
            int mch=L[crt].back().ind;
            L[crt].pop_back();
            if(elim[mch]==0){
                s[++vf]=nod;
                ok=1;
                elim[mch]=1;
                break;
            }

        }
        if(!ok)
        {
            ciclu[++k]=crt;
            vf--;
        }
    }
    for(i=1;i<k;i++)
        fout<<ciclu[i]<<" ";
    return 0;
}