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

#define N 100005

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int n, m;
vector < list <int> > a(N);
vector <int> gr(N, 0);
vector <bool> viz(N, 0);
queue <int> q;
stack <int> stk;

void bfs()
{
    q.push(1); viz[1] = 1;
    while(!q.empty())
    {
        int x = q.front(); q.pop();
        for( list <int> :: iterator it = a[x].begin(); it != a[x].end(); it++)
            if(!viz[*it])
            {
                viz[*it] = 1;
                q.push(*it);
            }
    }
}

bool ok()
{
    for(int i=1; i<=n; i++)
        if(gr[i] & 1 || (!viz[i] && gr[i]))
            return 0;
    return 1;
}

void Euler()
{
    stk.push(1);
    while(!stk.empty())
    {
        int x = stk.top();
        if(!a[x].size())
        {
            stk.pop();
            fout<<x<<' ';
        }
        else
        {
              int y = *a[x].begin();
              a[x].erase(a[x].begin());
              list <int> :: iterator it = a[y].begin();
              for(; it != a[y].end() && *it != x; it++);
              a[y].erase(it);
              stk.push(y);
        }
    }
}

int main()
{
    fin>>n>>m;
    while(m--)
    {
        int x, y;
        fin>>x>>y;
        if(x != y)
            gr[x]++, gr[y]++;
        a[x].push_back(y);
        a[y].push_back(x);
    }

    bfs();

    if(ok()) Euler();
    else fout<<(-1);

    return 0;
}