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

#define pii pair <int, int>
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)x.size()
#define pb push_back
#define fr first
#define sc second
#define vt vector
#define ub upper_bound
#define lb lower_bound

using namespace std;

string filename = "ciclueuler";
ifstream fin(filename + ".in");
ofstream fout(filename + ".out");

const int NMAX = 5e5;

pii edges[NMAX + 1];
vt <int> adj[NMAX + 1];

bool viz[NMAX + 1];

int main(){

    int n, m;
    fin >> n >> m;

    for(int i = 1; i <= m; i++){
        int a, b;
        fin >> a >> b;
        adj[a].pb(i);
        adj[b].pb(i);
        edges[i] = {a, b};
    }

    for(int i = 1; i <= n; i++){
        if(sz(adj[i]) % 2 == 1){
            fout << -1 << '\n';
            return 0;
        }
    }

    stack <int> S;
    S.push(1);

    vt <int> eul;
    while(!S.empty()){
        int node = S.top();

        if(sz(adj[node]) > 0){
            int vec = adj[node].back();
            adj[node].pop_back();

            if(!viz[vec]){
                viz[vec] = 1;
                int other = (edges[vec].fr ^ edges[vec].sc ^ node);
                S.push(other);
            }
        }else{
            eul.pb(node);
            S.pop();
        }
    }

    eul.pop_back();
    for(int x : eul){
        fout << x << ' ';
    }
    fout << '\n';

    return 0;
}