#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

int n, m;

struct mc
{
    int x, y, ind;
};

const int N = 5e5 + 5;

vector <mc> g[N];

int vis[N];

vector <int> cycle;

void euler(int node)
{
    while(g[node].size())
    {
        mc curr = g[node].back();
        g[node].pop_back();
        if(vis[curr.ind] == 0)
        {
            vis[curr.ind] = 1;
            euler(curr.y);
        }
    }
    cycle.push_back(node);
}
int main()
{
    in >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        in >> x >> y;
        g[x].push_back({x, y, i});
        g[y].push_back({y, x, i});
    }
    for(int i = 1; i <= n; i++)
    {
        if(g[i].size() % 2 == 1)
        {
            out << -1;
            return 0;
        }
    }
    euler(1);
    cycle.pop_back();
    for(auto x:cycle)
        out << x << ' ';
    return 0;
}