#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

const int NMax = 1e5, MMax = 5 * 1e5;

vector <int> g[NMax + 5], answer;
stack <int> st;
int n, m;
int from[MMax + 5], to[MMax + 5];
bool usenode[NMax + 5], useedge[MMax + 5];

void Read(){
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        fin >> x >> y;
        g[x].push_back(i);
        g[y].push_back(i);
        from[i] = x;
        to[i] = y;
    }
}

void DFS(int node){
    usenode[node] = 1;
    for (auto edge : g[node]){
        int ngh = from[edge] ^ to[edge] ^ node;
        if (!usenode[ngh])
            DFS(ngh);
    }
}

int Check(){
    DFS(1);
    for (int i = 1; i <= n; i++)
        if (g[i].size() % 2 || (g[i].size() && !usenode[i]))
            return 0;
    return 1;
}

void Cycle(int node){
    while (!g[node].empty()){
        int edge = g[node].back();
        g[node].pop_back();
        if (useedge[edge])
            continue;
        useedge[edge] = 1;
        st.push(node);
        node = from[edge] ^ to[edge] ^ node;
    }
}

void Solve(){
    int node = 1;
    do {
        Cycle(node);
        node = st.top();
        st.pop();
        answer.push_back(node);
    } while (!st.empty());
}

void Print(){
    for (auto node : answer)
        fout << node << ' ';
    fout << '\n';
}

int main(){
    Read();
    if (!Check())
        fout << -1 << '\n';
    else{
        Solve();
        Print();
    }
    return 0;
}