#include<iostream>
#include<fstream>
#include<vector>
#include<stack>
#define N 100010
#define M 500010
using namespace std;

ifstream f("ciclueuler.in");
ofstream o("ciclueuler.out");

vector <pair<int,int> > v[N];
int n,m;
bool viz[M];
void citire(){
    f>>n>>m; int i,x,y;
    for(i=1;i<=m;i++){
        f>>x>>y;
        v[x].push_back(make_pair(i,y));
        v[y].push_back(make_pair(i,x));
    }
}
void dfs(int k){
    pair<int,int> e;
    while(v[k].size()){
        e=v[k].back();
        v[k].pop_back();
        if(!viz[e.first]){
            viz[e.first]=1;
            dfs(e.second);
        }
    }
    o<<k<<" ";
}
int main(){
    citire();
    int i;
    for(i=1;i<=n;i++)
        if(v[i].size()%2==1){
            o<<-1;
            return 0;
        }
    dfs(1);
    o.close();
    f.close();
}