#include <fstream>
#include <vector>
#include <set>
#include <queue>
#include <stack>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

vector<multiset<int> >g;
int m, n, x, y;
queue<int>q;
stack<int>s;
bool vis[100001];
inline bool CheckEuler()
{
    q.push(1);
    for(;!q.empty();q.pop())
    {
        int x=q.front();
        for(multiset<int>::iterator it=g[x].begin(); it!=g[x].end(); it++ )
            if(!vis[*it])
            {
                vis[*it]=1;
                q.push(*it);
            }
    }
    for(int i = 1; i<= n; i++ )
        if(g[i].size()%2 || (!vis[i]&&g[i].size()) )
            return 0;
    return 1;
}

void Euler()
{
    s.push(1);
    for(;s.size();)
    {
        x = s.top();
        if (!g[x].size())
        {
            fout<<x<<" ";
            s.pop();
            continue;
        }
        int y = *g[x].begin();
        g[x].erase(g[x].begin());
        g[y].erase(g[y].find(x));
        s.push(y);
    }
}

int main()
{
    fin>>n>>m;
    g.resize(n+1);
    for(;m--;)
    {
        fin>>x>>y;
        g[x].insert(y);
        g[y].insert(x);
    }
    if(!CheckEuler())
        fout<<-1;
    else Euler();
    return 0;
}