#include <bits/stdc++.h>
using namespace std;

#define N 100010
int n, m;
vector <int> sol, v[N];
stack <int> S;

struct edge{
    int a, b, c;
} M[5*N];

int nxt(int nod, int i){
    if (nod == M[i].a) return M[i].b;
    return M[i].a;
}

int main(){
    ifstream cin ("ciclueuler.in");
    ofstream cout ("ciclueuler.out");
    cin >> n >> m;
    for (int i=1; i<=m; i++){
        int x, y;
        cin >> x >> y;
        v[x].push_back(i);
        v[y].push_back(i);
        M[i] = {x, y, 1};
    }
    for (int i=1; i<=n; i++){
        if (v[i].size()%2){
            cout << -1;
            return 0;
        }
    }
    S.push(1);
    while (!S.empty()){
        int nod = S.top();
        int i = 0;
        while (i < v[nod].size() && !M[v[nod][i]].c) i++;
        if (i >= v[nod].size()) S.pop(), sol.push_back(nod);
        else S.push(nxt(nod, v[nod][i])), M[v[nod][i]].c = 0;
    }
    for (auto it: sol) cout << it << " ";
    return 0;
}