#include <bits/stdc++.h>
#define ll long long
#define mp make_pair
#define pb push_back
#define mod 1000000007
 
using namespace std;

int n, m;
vector < int > V[500100];
int x[500500], y[500500];
bool v[500500];
string rs;

void euler(int node)
{
    for (auto it : V[node])
        if (!v[it]) v[it] = 1, euler(x[it] ^ y[it] ^ node);
    rs += to_string(node) + " ";
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    ifstream cin("ciclueuler.in");
    ofstream cout("ciclueuler.out");
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        cin >> x[i] >> y[i];
        V[x[i]].pb(i);
        V[y[i]].pb(i);
    }
    for (int i = 1; i <= n; i++) if (V[i].size() & 1) return cout << -1, 0;
    euler(1);
    for (int i = rs.size()-2; i; i--) cout << rs[i];
    return 0;
}