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

const int NMAX = 1e5;
vector<int>v[NMAX+1];
unordered_map<int,int>vap[NMAX+1];
int n,m,k;
int ans[5*NMAX+1];
int rang[NMAX+1];
void read()
{
    cin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int st,dr;
        cin >> st >> dr;
        v[st].push_back(dr);
        v[dr].push_back(st);
        vap[st][dr]++;
        vap[dr][st]++;
        rang[st]++;
        rang[dr]++;
    }
}

void dfs(int nod)
{
    for(int i : v[nod])
    {
        if(vap[nod][i] > 0)
        {
            vap[nod][i]--;
            vap[i][nod]--;
            dfs(i);
        }
    }
    ans[++k] = nod;
}

void solve()
{
    for(int i = 1; i <= n; i++)
        if(rang[i] % 2 != 0)
        {
            cout << -1;
            return;
        }

    dfs(1);
    if(k != m+1)
        cout << -1;
    else
    {
        for(int i = 1; i <= k; i++)
            cout << ans[i] << ' ';
    }
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    read();
    solve();
}