# pragma GCC optimize("O3")
# include <bits/stdc++.h>
# define maxn 100001
# define ll long long
# define clock (clock() * 1000.0 / CLOCKS_PER_SEC)
# define rc(s) return cout << s,0
# define _ ios_base::sync_with_stdio(false);cin.tie(0);cerr.tie(0);cout.tie(0);
# define pb push_back
# define mp make_pair
//# define int ll
using namespace std;

vector<pair<int,int>>vec[maxn];
int n,m,x,y;
vector<int>ans;
bool viz[maxn * 5];

void dfs(int nod)
{
    for(auto it : vec[nod])
    {
        if(!viz[it.second])
		{
			viz[it.second] = 1;
			dfs(it.first);
		}
    }
    ans.pb(nod);
}

int32_t main(){_
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
	cin >> n >> m;
	for(int i = 1;i <= m;i++)
	{
		cin >> x >> y;
		vec[x].pb(mp(y,i));
		vec[y].pb(mp(x,i));
	}
	for(int i = 1;i <= n;i++)
		if((int)vec[i].size() & 1) rc(-1);
    dfs(1);
    for(auto it : ans) cout << it << ' ';
}