#include <bits/stdc++.h>
//Soltan Cristian
#define fri(a, b) for (int i = (a); i < (b); ++i)
#define frj(a, b) for(int j = a; j < b; j++)
#define frk(a, b) for(int k = a; k < b; k++)
#define frm(a, b, i) for(int i = b; i >= a; i--)
#define ll long long
#define all(x) x.begin(), x.end()
#define mod 1000000007
#define pb push_back
#define st first
#define nd second
#define sz(x) (ll)x.size()
#define rall(x) x.rbegin(), x.rend()
#define ct(x) cout << x
#define cts(x) cout << x << ' '
#define ctn(x) cout << x << '\n'
#define Y cout << "YES" << '\n'
#define N cout << "NO" << '\n'
using namespace std;
using vi = vector<int>;
using vl = vector<ll>;
using vs = vector<string>;
using vb = vector<bool>;
using ml = map<ll, ll>;
using vii = vector<vector<int>>;
using vll = vector<vector<ll>>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
template <typename T>void read(T n, vector<T> &a){fri(0, n){cin >> a[i];}}
template<typename T>void print(T n, T m, vector<vector<T>> &dp){fri(0, n){ct('\n');frj(0, m){ct(setw(5));cts(dp[i][j]);}}}



const int mxa = 1e5 + 1;
string __fname = "ciclueuler";  
ifstream in(__fname + ".in"); 
ofstream out (__fname + ".out"); 
#define cin in 
#define cout out
pii edge[5 * mxa];
vi adj[mxa];
vi used(5 * mxa);



void solve(){
    int n, m;
    cin >> n >> m;
    fri(0, m){
        int a, b;
        cin >> a >> b;
        adj[a].pb(i);
        adj[b].pb(i);
        edge[i] = {a, b};
    }
    fri(0, n){
        if(sz(adj[i]) % 2 != 0){
            cout << -1 << '\n';
            return;
        }
    }
    stack<int> s;
    vector<int> ans;
    s.push(1);
    while(!s.empty()){
        int u = s.top();
        if(sz(adj[u]) == 0){
            ans.pb(u);
            s.pop();
        }
        else{
            int cat = adj[u].back();
            adj[u].pop_back();
            if(used[cat]){
                continue;
            }
            if(u == edge[cat].st){
                s.push(edge[cat].nd);
            }
            else{
                s.push(edge[cat].st);
            }
            used[cat] = 1;
        }
    }
    ans.pop_back();
    for(auto i: ans){
        cout << i << ' ';
    }
    cout << '\n';
}


int main()
{   
    ios_base::sync_with_stdio(0); cin.tie(0); ct(fixed); ct(setprecision(10)); 
    // int t;
    // cin >> t;
    // while(t--)
        solve();
    return 0;
}