#include <bits/stdc++.h>

using namespace std;

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

const int N = 1e5 + 1, M = 5e5;
int n, m, x, y, grad[N], poz[N];
pair<int, int> muchie[M];
vector<int> incidenta[N], ans;
bitset<M> sters;
stack<int> s;

bool gradePare(){
    for(int i = 1; i <= n; i++){
        if(grad[i] % 2)
            return 0;
    }

    return 1;
}

int cautMuchie(int x){
    for(int i = poz[x]; i < incidenta[x].size(); i++){
        if(!sters[incidenta[x][i]]){
            poz[x] = i + 1;
            return incidenta[x][i];
        }
    }

    return -1;
}

int main(){
    f >> n >> m;
    for(int i = 0; i < m; i++){
        f >> x >> y;
        muchie[i] = {x, y};
        incidenta[x].push_back(i);
        incidenta[y].push_back(i);
        grad[x]++;
        grad[y]++;
    }

    f.close();
    if(!gradePare()){
        g << -1;
        return 0;
    }

    s.push(1);
    while(!s.empty()){
        x = s.top();
        int e = cautMuchie(x);
        if(e == -1){ //
            s.pop();
            if(!s.empty()) // vrem sa nu scriem primul element si la sfarsit
                ans.push_back(x);
        }else{
            sters[e] = 1;
            y = muchie[e].first + muchie[e].second - x;
            s.push(y);
        }
    }

    if(ans.size() < m){ // graful are mai multe cicluri disjuncte
        g << -1;
    }else{
        for(int x: ans)
            g << x << ' ';
    }
}