#include <fstream>
#include <stack>
#include <vector>
#include <algorithm>
#define NMAX 100005
using namespace std;

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

vector<int> G[NMAX];
int n, m;

void read_data(){
    f >> n >> m;
    for(int i = 1; i<=m; i++){
        int x, y;
        f >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
    }
}


bool check_euler(){
    for(int i = 1; i<=n; i++){
        if(G[i].size() % 2 != 0){
            return false;
        }
    }
    return true;
}

vector<int> euler_cycl(){
    vector<int> sol;
    if(!check_euler()){
        return {-1};
    }
    stack<int> st;
    st.push(1);
    while(!st.empty()){
        int node = st.top();
        if(!G[node].empty()){
            int new_node = G[node].back();
            G[node].pop_back();
            G[new_node].erase(find(G[new_node].begin(), G[new_node].end(), node));
            st.push(new_node);
        }
        else{
            sol.push_back(node);
            st.pop();
        }
    }
    return sol;
}

int main(){
    read_data();
    auto sol = euler_cycl();
    for(const auto& elem:sol){
        g << elem << ' ';
    }
    return 0;
}