#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;

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

const int NMAX = 100005, MMAX = 500005;
vector<int> G[MMAX];
vector<int> rez;
pair<int,int> muchii[MMAX];

void findEuler(int startNode){
    bool used[MMAX] = {false};
    stack<int> st;
    st.push(startNode);

    while(!st.empty()){
        int nod = st.top();

        if(!G[nod].empty()){

            int indiceMuchie = G[nod].back();
            G[nod].pop_back();

            if(!used[indiceMuchie]){
                used[indiceMuchie] = true;
                
                int u = muchii[indiceMuchie].first;
                int v = muchii[indiceMuchie].second;

                int nodUrmator = (nod == u) ? v : u;

                st.push(nodUrmator);
            }
        }
        else{
            st.pop();
            rez.push_back(nod);
        }
    }
}


int main(){
    int n,m;
    f >> n >> m;
    for(int i=1; i<=m; i++){
        int x,y;
        f >> x >> y;
        G[x].push_back(i);
        G[y].push_back(i);
        muchii[i] = {x,y};
    }
    for(int i=1; i<=n; i++){
        if(G[i].size() & 1){
            g << -1;
            return 0;
        }
    }

    findEuler(1);
    for(int i=0; i<rez.size(); i++){
        g << rez[i] << " ";
    }

    return 0;
}